How and Why Wonder Book of the Microscope

7 m H

O

W

A

N

D

W

H

Y

U/onda/iBoo&ofr

T h e ,

I

M

i

M

i

M

r

A N D

t

W H A T

Y O U

/ / ! ' _ \J? 0W'

^

**d Why Wonder^ A

S E E

T H E

T

h

H O W

e

A N D

A N D

W H Y

W O N D E R

B O O K

,

W H A T

Y<

W r i t t e n by M A R T I N

KEEN

I l l u s t r a t e d by W A L T E R

FERGUSON

Editorial Production: D O N A L D

D. W O L F

E d i t e d u n d e r t h e s u p e r v i s i o n of Dr. P a u l E. B l a c k w o o d Specialist for Elementary Science U. S. D e p a r t m e n t of H e a l t h , E d u c a t i o n a n d W e l f a r e W a s h i n g t o n , D. C . T e x t a n d i l l u s t r a t i o n s a p p r o v e d by O a k e s A. W h i t e Brooklyn Children's Museum Brooklyn, New York WONDER

BOOKS

•

NEW

YORK

O F

Introduction The How and Why Wonder Book of the Microscope i n t r o d u c e s o n e of the i n s t r u m e n t s that h a s b e e n m o s t i m p o r t a n t to scientists in their nevere n d i n g search for a c c u r a t e k n o w l e d g e a b o u t o u r world. T h e i n s t r u m e n t helps o u r eyes, wonderful as they are, to b e even m o r e wonderful, b y extending the sense of sight. It brings before o u r eyes the w o r l d of invisible life, the world of tiniest p l a n t s a n d animals, t h e bacteria a n d protozoa. Indeed, the m i c r o s c o p e m a k e s the " u n s e e n w o r l d " visible. B u t to get full p l e a s u r e a n d benefit from this r e m a r k a b l e i n s t r u m e n t requires k n o w l e d g e of h o w to o p e r a t e it carefully. It requires p r a c t i c e in focusing light a n d in p r e p a r i n g specimens for e x a m i n a t i o n . T h i s b o o k will help the beginning microscopist learn these things. A n d it gives directions for using the m i c r o s c o p e to observe the details of m a n y c o m m o n things all a r o u n d us. A p a g e of this b o o k suddenly b e c o m e s a m a s s of stringy fibers, while the surface of a tree leaf b e c o m e s a m i r a c l e of designs w h e n viewed through a microscope. E v e r y y o u n g scientist h a s a h e a d of him m a n y exciting experiences exploring t h e u n s e e n world. The How and Why Wonder Book of the Microscope, like t h e o t h e r p u b l i c a t i o n s in the series, is a useful t e a c h e r a n d guide in t h a t exploration. Paul E. Blackwood Specialist for Elementary Science U.S. Department of Health, Education and Welfare Washington, D. C. ff

© 1961, by Wonder Books, Inc. All rights reserved under International and Pan-American Copyright Conventions. Published simultaneously in Canada. Printed in the United States of America.

Contents Page AN UNSEEN WORLD

4

THE MICROSCOPE What is a microscope? How does it work? What is a simple microscope? What can you see with a simple microscope? How can you keep a record of what you see? What is a focus? How can you make a water-lens microscope? Who invented the microscope? What is a microscopist? How was diamond dust used for a microscope? What objects did he study?

5 5 5 6 7 8 9 10 11 11

THE COMPOUND MICROSCOPE What is a compound microscope? What are the two systems of lenses? What are some parts of a compound microscope? How do you find out the magnifying power of a microscope? What are the other parts of a compound microscope? How do you use a laboratory compound microscope? How do you focus it? How do you clean the equipment? What equipment will you need to become a microscopist? What kind of microscope should you get?

12 12 13

THE WORLD OF INVISIBLE L I F E BACTERIA AND PROTOZOA What are the smallest plants in the world? Where are bacteria found? How are bacteria useful? What do bacteria look like? When do they thrive best? What is the process of pasteurization? How fast do bacteria reproduce? How can you get bacteria? How do you prepare bacteria for the microscope? How can you stain bacteria? How can you prepare a stained slide? What is a hanging drop mount? How can you make your own hanging drop mount? What are the smallest animals in the world? What do the protozoa eat? How can you examine protozoa? How can you keep protozoa in place? How do protozoa move about?

12 12

13 14 14 15 17 17 18 18 19 19 19 19 20 20 21 21 21 22 23 24 24 25 25 26 26 27 27

Page What is a Peranema? 28 What is an amoeba? 28 How does an amoeba move? 28 What is a paramecium? 28 What is inside a protozoan? 29 How do protozoa collect wastes and water? 29 How does the amoeba eat? 30 How does a paramecium get its food? 30 How can you feed protozoa? 30 How do bacteria and protozoa suspend life? 31 Where do hay-infusion bacteria and protozoa come from? 31 How do the number of bacteria and protozoa increase? 31 How do they reproduce? 32 What kind of microscopic plants live in "houses"? 33 MOLDS, MILDEW, YEAST BUDDING How can you grow plants on a slice of bread? What do molds look like? How are molds useful to man? What is mildew? What is yeast budding? How else does yeast budding differ from cell division? How are yeasts useful to man? How can you see fermentation?

34 34 35 35 35 37

INSECTS Where can you keep insects? What does a fly's eye look like? How can a fly walk upside down?

39 39 39 40

FABRICS How is cotton thread made? How do natural fibers differ from man-made (artificial) ones? How is muslin woven? How is knitted fabric made?

40 40

BLOOD What does blood do? What is blood made of? How can you get a sample of your blood? How do you make a blood smear? What do blood cells look like? How can you see blood in circulation? How can you observe the insides of living things? THE ELECTRON MICROSCOPE What are the limitations of optical microscopes? What is an electron microscope? How does this microscope help man?

38 38 39

A n

T h e h u m a n e y e is a w o n d e r f u l

U n s e e n

W o r l d

organ.

t h e r e a r e m a n y things t h e y c a n n o t en-

O u r e y e s tell u s m o r e a b o u t t h e w o r l d

a b l e u s t o see. A m o n g t h e s e a r e v e r y

a r o u n d u s t h a n a n y of o u r o t h e r s e n s e

small

things.

o r g a n s d o . T h e size a n d s h a p e of t h i n g s ,

about

small

Usually, things,

when

we

we

mean

talk things

their color, their distance from us, a n d

a b o u t t h e size of t h e p e r i o d a t t h e e n d

w h e t h e r o n e o b j e c t is in f r o n t o r i n b a c k ,

of t h i s s e n t e n c e . N o w , y o u c a n s e e t h e

a b o v e o r b e l o w , a r e all t h i n g s w e l e a r n

p e r i o d q u i t e e a s i l y , a n d if it w e r e o n l y

b y u s i n g o u r eyes. W e c a n see t h i n g s

o n e - t e n t h i t s size, y o u c o u l d still see it.

t h a t a r e o n l y a f e w i n c h e s in f r o n t of

B u t if t h e p e r i o d

o u r eyes, a n d then w e c a n look o u t the

d r e d t h of its p r e s e n t

w i n d o w a n d i n s t a n t l y see things m o r e

p r o b a b l y l o s e s i g h t of it. Y e t , s m a l l a s

than a mile away.

t h e s h r u n k e n p e r i o d m i g h t b e , it w o u l d

Y e t , r e m a r k a b l e as o u r eyes m a y be,

still b e m u c h

shrank

to

one-hun-

size, y o u

larger than

would

millions

of

Microorganisms are organisms of microscopic size.

s * ; :'^pHffflf. •

1 2 3 4

FAIRY SHRIMP DINOFLAGEUATE HYDROIDS NEMATODE

5 6 7 8

NOCTILUCA PLANARIAS PROTOMYXA HAIOSPHAERA

different

k i n d s of t h i n g s t h a t e x i s t in

your everyday world. T h e r e are certain plants — which we shall soon learn a b o u t — that are

so

s m a l l y o u c o u l d p u t 2 5 0 , 0 0 0 of t h e m o n t h e p e r i o d a t t h e e n d of t h i s s e n t e n c e . And much

there

are

animals

that

are

not

bigger.

N o m a t t e r h o w closely you look at t h e s h e e t of p a p e r o n w h i c h t h e s e w o r d s a r e p r i n t e d , it will still l o o k like a f a i r l y s m o o t h s u r f a c e , b u t if y o u r e y e s c o u l d see m u c h s m a l l e r t h i n g s t h a n t h e y n a t u rally can, y o u w o u l d see t h a t t h e p a p e r

learn about these details? W h a t can we

is r e a l l y a t w i s t e d m a s s of

u s e t o a i d o u r e y e s in s e e i n g t h e u n s e e n

fibers.

T h e r e a r e h u n d r e d s of d e t a i l s a b o u t the world that are t o o small for

your

u n a i d e d e y e s t o see. H o w , t h e n , d o w e

T h e

ing

at

small

things.

The word

microscope

comes

two

from

c i e n t G r e e k w o r d s , mikros, " s m a l l , " a n d skopein,

called a

instrument

microscope.

W h e n w e s e e a n y t h i n g , w e d o so b e How does it work?

an-

which means

which means "to

cause from

light

is

reflected

the object to

our

e y e s . If t h e r a y s of l i g h t

c o m e straight from the object to

our

eyes, w e see t h e o b j e c t in its n a t u r a l size. B u t if t h e r a y s of l i g h t c o m i n g t o

look at." in

o u r e y e s a r e b e n t in a c e r t a i n w a y , t h e n

more

the object looks bigger. W h e n this hap-

All microscopes have one thing common:

a r o u n d us? W e can use an

M i c r o s c o p e

A m i c r o s c o p e is a n i n s t r u m e n t for lookWhat is a microscope?

w o r l d of v e r y s m a l l t h i n g s t h a t a r e all

They contain

p a r t s c a l l e d lenses.

one or

A l e n s is a n y c l e a r

p e n s , w e s a y t h e o b j e c t is magnified.

A

s u b s t a n c e t h a t h a s a definite s h a p e a n d

l e n s of t h e p r o p e r s h a p e c a n b e n d l i g h t ,

will b e n d l i g h t r a y s a s t h e y p a s s t h r o u g h

s o t h a t t h i n g s w e see t h r o u g h t h e l e n s

it. M o s t l e n s e s a r e m a d e of g l a s s ,

a r e m a g n i f i e d . A n y l e n s t h a t d o e s t h i s is

but

a l e n s c o u l d b e m a d e of w a t e r , of oil, o r of c l e a r p l a s t i c .

a microscope. Y o u m a y w o n d e r if l e n s e s c a n a l s o

H

LINEN TESTER

m a k e things look smaller. T h e answer is " y e s . " Y o u c a n e a s i l y p r o v e t h i s b y l o o k i n g t h r o u g h t h e l a r g e e n d of a h a n d t e l e s c o p e o r a p a i r of

field

glasses.

M i c r o s c o p e s t h a t a r e m a d e of o n e , o r

these are

examples

of

simple

micro-

p e r h a p s two, lenses are

scopes.

usually

magni-

is m a d e u p of o n e o r m o r e l e n s e s t h a t

or

hand

s h o w y o u a magnified object right-side-

These

are

u p a n d in the s a m e place w h e r e

are

w o u l d s e e it w i t h o u t t h e l e n s . Y o u w i l l

also microscopes. H a v e y o u ever seen

u n d e r s t a n d this definition better w h e n

t h e m a g n i f y i n g g l a s s u s e d b y s t a m p col-

w e l e a r n a b o u t t h e o t h e r k i n d of m i c r o -

l e c t o r s ? I t is m a d e u p of j u s t o n e

scope.

What is a simple microscope?

fying

called

glasses,

lenses. p r o p e r n a m e s for

ft

FINGERPRI

There are many kinds of instruments for looking at small things—used by detectives and others.

them, but they

or

A s i m p l e m i c r o s c o p e is o n e t h a t

you

t w o s m a l l l e n s e s fixed i n a m e t a l f r a m e

Y o u c a n b u y a single- o r double-lens

a n d h e l d i n t h e h a n d of t h e p e r s o n u s i n g

m i c r o s c o p e in almost a n y toy store or

it. H a v e y o u e v e r seen a j e w e l e r o r a

five-and-ten-cent store. Such

watchmaker

a

s c o p e s r a n g e in p r i c e f r o m less t h a n a

snouty-looking

dollar to three or four dollars. T h e very

o b j e c t h e l d a t o n e eye?" T h i s is a m i c r o -

c h e a p ones m a y h a v e p o o r l y - m a d e glass

s c o p e c a l l e d a loupe.

lenses

looking

at

watch through a black,

picture

of

the

Holmes holding

a

or

D i d y o u e v e r see a

detective a

gem

round

or

plastic

lenses

that

micro-

scratch

Sherlock

e a s i l y . A d o l l a r a n d a h a l f is p r o b a b l y

magnifying

the price for w h i c h you can b u y a very

g l a s s fixed i n a c i r c u l a r b a n d of m e t a l

useful h a n d lens, s u c h as is u s e d

and attached to a short handle?

s t a m p collectors.

All

by

When you have obtained your microscope, What can you see with a simple microscope?

simple

you

u s e it t o l e a r n

can things

a b o u t your daily world that you

never

knew

before. O b t a i n a mag-

will see t h a t t h e r e a r e m o r e r e d

dots

c r o w d e d closer t o g e t h e r in o r d e r t o produce the redder color. O p e n your handkerchief and look at i t a s y o u h o l d it u p t o t h e l i g h t .

You

c a n e a s i l y s e e t h a t it is w o v e n of t h o u -

azine with a smooth, or slick, p a p e r c o v e r t h a t b e a r s t h e c o l o r p h o t o g r a p h of a p e r s o n . T h e of

the

slick

paper

majority

magazines

have

covers like this. W i t h y o u r m i c r o s c o p e , e x a m i n e t h e f a c e of t h e p e r s o n i n t h e p i c t u r e . Y o u w i l l s e e t h a t t h e c o l o r of

t f -iSwfr

L

i r mnjtj

n Hwni

i j i WKJJT—»

t h e flesh of t h e f a c e is m a d e u p of m a n y t i n y d o t s o r s p e c k s of d i f f e r e n t

colors.

'**'*"" M&tfiji'

T h e r e are red, yellow, a n d green or blue

>4 ,

1 v-4

-J j j—I

_

I 0||4.—

d o t s , a n d t h e w h i t e c o l o r of t h e p a g e *i—I-

shows t h r o u g h in spaces n o bigger t h a n the colored dots. T a k e the

magnifying

lens a w a y a n d look at the p a g e with

-]—L t ~

r

1 — I •"

A swatch of wool under a microscope shows its weave. Cotton gabardine twill as viewed under a microscope.

y o u r u n a i d e d eye. Y o u will see h o w t h e c o m b i n a t i o n of t h e s e d o t s , t o o s m a l l t o b e seen w i t h o u t the m i c r o s c o p e , b l e n d s t o g e t h e r t o p r o d u c e t h e c o l o r of

flesh.

W i t h the microscope, look at the red a r e a of t h e c h e e k o r a t t h e l i p s .

You

Newspaper print looks like this when it is magnified.

s a n d s of t h r e a d s . N o w u s e y o u r m i c r o scope to look at the handkerchief. Y o u w i l l s e e h o w e a c h t h r e a d is w o v e n ,

first

under, then over, the threads near

it.

N o t e t h a t all t h e t h r e a d s a r e n o t e q u a l l y t h i c k . Y o u w i l l s e e t h a t m o s t of t h r e a d s look fuzzy b e c a u s e from sides tiny, frayed

filaments

the their

of fiber s t i c k

out. L o o k a t s e v e r a l d i f f e r e n t s a m p l e s of

m * * • <

Amethyst crystal's form when magnified.

When you look at this print of a baby under a microscope, you can see that it is made up of many dots. cloth that have colored patterns. c a n y o u tell w h i c h

samples have

How the

color printed on them and which have the color woven into them? Y o u

Y o u will a d d g r e a t l y t o y o u r

can

and H o w can you keep a record - . _ of w h a t y o u s e e ?

y o u r m i c r o s c o p e . If, a s f a r a s y o u c a n follow t h e t h r e a d , it is o n e c o l o r , t h e n the cloth has a woven pattern. O n the o t h e r h a n d , if y o u t r a c e a s i n g l e t h r e a d a n d find t h a t it is c o l o r e d d i f f e r e n t l y i n d i f f e r e n t p a r t s of t h e p a t t e r n , t h e n t h e pattern was printed on the cloth. Your

microscope

will

reveal

d r e d s of n e w t h i n g s , if y o u a

stone

that

has

carefully different

c o l o r s i n it. L o o k a t t h e s m a l l h a i r s o n t h e b a c k of y o u r h a n d . E x a m i n e a p i e c e of w o o d a l o n g t h e s u r f a c e w h e r e a c a r p e n t e r h a s s a w e d it. L o o k a t t h e l e g of a n insect. 8

w o r k i n g

. ., with

a

micro-

s c o p e , if y o u k e e p a r e c o r d of w h a t y o u see. Y o u c a n k e e p such a record in a n o t e b o o k or o n

file

c a r d s t h a t a r e five i n c h e s l o n g a n d t h r e e inches wide. B o t h the notebook and the c a r d s c a n b e b o u g h t i n a l m o s t a n y stationery or

five-and-ten-cent

store.

H e r e are the things to p u t in y o u r hun-

e x a m i n e t h e o b j e c t s of y o u r d a i l y w o r l d . Examine

knowledge

w h e n

d o this b y tracing a single t h r e a d w i t h

interest

record book or cards: Examination Date

number

of examination

Object

examined

Where

I found

What Remarks

I saw

. . . . . .

. . . it . . .

. . .

. . .

Under remarks, you might want

to

An image out of focus (left). Image now in focus (right).

Diagram (left): light passing through simple microscope. write something

like:

"Compare

this

Y o u r eye h a s a lens. T h i s lens covers

For

t h e p a r t of y o u r e y e t h a t is c o l o r e d a n d

example, you m a y have just examined

also the d a r k spot, t h e pupil, at its cen-

t h e a n t e n n a of a b u t t e r f l y , a n d

some

ter. L i k e all lenses, t h e o n e in y o u r eye

time before, you h a d e x a m i n e d the an-

b e n d s r a y s of l i g h t . T h e l i g h t is b e n t s o

t e n n a of a m o t h . Y o u w o u l d p r o b a b l y

t h a t i t falls o n t h e b a c k of y o u r

eye

w a n t t o m a k e n o t e of t h e f a c t t h a t t h e

w h e r e light-sensitive materials a r e

lo-

a n t e n n a s of t h e s e t w o k i n d s of i n s e c t s

cated. W h e n the lens in y o u r eye w o r k s

are quite

j u s t r i g h t , it b e n d s l i g h t so t h a t

with Examination n u m b e r

different.

So,

"

on

the

card

each

b e a r i n g y o u r r e c o r d of t h e e x a m i n a t i o n

light ray entering y o u r eye from a n ob-

of t h e b u t t e r f l y ' s a n t e n n a , y o u r e f e r t o

ject falls e x a c t l y in t h e p r o p e r p l a c e t o

t h e c a r d b e a r i n g t h e r e c o r d of t h e e x a m -

g i v e a s h a r p i m a g e of t h e o b j e c t o n t h e

i n a t i o n of t h e m o t h ' s a n t e n n a ; a n d o n

b a c k of t h e e y e . A s l o n g a s t h e p o i n t

the moth's card, you refer to the butter-

w h e r e the light rays form a s h a r p image

fly. C r o s s - r e f e r e n c e s l i k e t h i s w i l l g r e a t l y

is e x a c t l y o n t h e b a c k of t h e e y e , w e

i n c r e a s e y o u r k n o w l e d g e of t h e t h i n g s

s e e t h e o b j e c t s h a r p l y a n d c l e a r l y . If t h i s

you examine.

p o i n t is t o o f a r f o r w a r d o r t o o f a r b a c k , objects w e see are fuzzy a n d

W h e n you were examining things with u r

»A,L . •

y°

a focus?

y o u

P

T h i s is w h a t h a p p e n s t o n e a r - a n d far-

microscope,

sighted persons. T h e point at which a

y noticed that

l e n s f o r m s a s h a r p i m a g e is c a l l e d t h e

simple r o b a b l

blurred.

y o u c o u l d n o t see clearly

focus

of t h e l e n s .

w h e n y o u h e l d t h e l e n s j u s t a n y o l d dis-

T h e l e n s of y o u r m i c r o s c o p e a l s o h a s

tance from the object. Y o u h a d to m o v e

a focus. Y o u h a d t o m o v e the micro-

the lens b a c k a n d forth until the object

s c o p e b a c k a n d f o r t h u n t i l t h e f o c u s of

b e c a m e clear. W h y w a s this necessary?

its lens w a s exactly w h e r e it c o u l d w o r k

w i t h t h e lens in y o u r eye, so as t o f o r m

a water lens can also be m a d e . W i t h a

a s h a r p i m a g e o n t h e b a c k of y o u r e y e .

h e a v y shears, cut a strip from a tin can.

W e c a l l t h e m o v i n g b a c k a n d f o r t h of a

T h i s tin strip should b e a b o u t o n e inch

l e n s t o f o r m a s h a r p i m a g e focusing

w i d e a n d four inches long. B e careful

the

n o t to cut yourself on the sharp edges

lens.

of t h e t i n . W h e n t h e s t r i p is c u t , d u l l W i t h a p a i r of p l i e r s , s t r a i g h t e n o u t a paper H o w can you make a water, . „ lens microscope?

p i e c e

clip or of

. ., similar

w k e

a of

. . , thickness.

t h e e d g e s w i t h a file, o r c o v e r t h e e d g e s with adhesive tape. M a r k t h e e x a c t c e n t e r of t h e t i n s t r i p . P l a c e t h e s t r i p o n a p i e c e of w o o d , a n d

A t o n e e n d of t h e wire, b e n d a complete loop a b o u t one-

drive a medium-size nail through the

s i x t e e n t h of a n i n c h a c r o s s . R u b a l i t t l e

a h o l e m o r e t h a n o n e - s i x t e e n t h i n c h in

g r e a s e o r c o o k i n g oil o n t h e l o o p . D i p

diameter. R e m o v e the nail and the piece

t h e l o o p i n w a t e r a n d g e n t l y r e m o v e it.

of w o o d .

c e n t e r . D o n o t u s e a n a i l t h a t will m a k e

W i t h i n t h e l o o p w i l l b e a d r o p of w a t e r

B e n d t h e e n d s of t h e s t r i p d o w n w a r d ,

t h a t forms a lens. L o o k at t h e p r i n t o n

so t h a t t h e strip will s t a n d . A s w i t h t h e

a p a g e t h r o u g h the w a t e r lens. T h e lens

l o o p m i c r o s c o p e , r u b a little grease o r

will p r o b a b l y m a g n i f y t h e p r i n t t o twice

oil a r o u n d t h e h o l e in t h e strip. S t a n d

i t s n a t u r a l size. E v e n t u a l l y , t h e

water

t h e strip o n its t w o e n d s . D i p a pencil

w i l l e v a p o r a t e , b u t it is e a s y t o m a k e

i n w a t e r a n d c a r e f u l l y r e m o v e it. T r a n s -

a n o t h e r w a t e r lens.

f e r a d r o p of w a t e r f r o m t h e e n d of t h e

A d i f f e r e n t k i n d of m i c r o s c o p e w i t h

pencil t o t h e hole, so t h a t a d r o p h a n g s in the hole, f o r m i n g a lens. P l a c e a s m a l l p a n e of w i n d o w g l a s s o n t h e t o p s of t w o t i n c a n s of t h e s a m e

WATER DROP

BENT TIN STRIP WINDOW GLASS PANE

SALT CRYSTALS MAGNIFIED TIN CAN

LIGHT REFLECTED FROM MIRROR

10

The first microscopist was Antony van Leeuwenhoek, a cloth merchant from Holland. He is pictured here with the microscope of his design, (b. 1632,d. 1723)

size. P l a c e t h e t i n s t r i p c a r e f u l l y o n t h e

a l e n s a t o n e e n d . T h e s e w e r e c a l l e d flea

c e n t e r of t h e g l a s s . B e n e a t h t h e g l a s s ,

g l a s s e s o r fly g l a s s e s , a n d t h e s e n a m e s

p r o p a flat m i r r o r , s u c h a s is f o u n d in

show

l a d y ' s h a n d b a g s , s o t h a t l i g h t is r e f l e c t e d

scopes w e r e u s e d for.

pretty

well

what

these

micro-

u p w a r d t h r o u g h the glass a n d the water lens.

Although we do not know who invented

B e n e a t h the lens, place a few grains of p e p p e r , s a l t , o r s u g a r , a n d l o o k d o w n through

the lens. F o c u s

the lens

by

What is a microscopist?

the microscope, we do k n o w w h o w a s t h e first microscopist.

A

micro-

gently pressing o n the strip. H o w m a n y

s c o p i s t is a p e r s o n w h o u s e s a m i c r o -

times d o you think the w a t e r lens mag-

s c o p e t o s t u d y small t h i n g s in a careful

nified t h e g r a i n s ?

a n d s y s t e m a t i c w a y . If y o u s t u d y t h i n g s carefully with y o u r simple microscope

W e don't k n o w just w h o m a d e the Who invented the microscope?

first

a n d k e e p a r e c o r d of y o u r

findings,

you

microscope. In the

a r e a m i c r o s c o p i s t . T h e first m i c r o s c o -

thirteenth

pist w a s A n t o n y van L e e u w e n h o e k .

a

century,

monk

named

V a n L e e u w e n h o e k was a cloth mer-

B a c o n

c h a n t w h o lived in Delft, H o l l a n d d u r -

learned h o w to g r i n d glass to m a k e spec-

i n g m o s t of t h e s e v e n t e e n t h c e n t u r y a n d

tacles. A little while a f t e r w a r d , gentle-

p a r t of t h e e i g h t e e n t h . H e l i v e d a q u i e t

men carried about with them a

small

life a s a t r a d e s m a n , b u t h e w a s , i n h i s

m i c r o s c o p e t h a t - c o n s i s t e d of a

metal

s p a r e t i m e , o n e of t h e w o r l d ' s

R o g e r

t u b e , a b o u t t h e size of y o u r t h u m b , w i t h

great

scientific d i s c o v e r e r s . 11

He

obtained

diamond

dust from diamond

How was diamond dust used for a microscope?

of

the

cutters

Delft

with

H e s t u d i e d t h e e y e s of a s h r i m p , c o d f i s h , whale, rabbit,

What objects did he study?

a n d beetle. H e studied t h e e g g s of a n t s a n d

which he ground a

nearly-spheri-

cow,

lice. Seeds, b l o s s o m s , fruits, a n d

other

cal lens. H e m o u n t e d t h e lens o n a de-

p a r t s of t h e p l a n t ; t h e c i r c u l a t i o n

vice that

b l o o d i n t h e t a i l of a fish; t h e t a r t a r o n

included

a

metal

rod

into

of

which a screw-thread was cut. B y turn-

t h e t e e t h of a n e i g h t - y e a r - o l d b o y

ing the rod, he could m a k e very

t w o ladies; v i n e g a r eels, crabs, a n d oys-

fine

and

focusing a d j u s t m e n t s for his lens. T h e

ter eggs — all t h e s e w e r e a m o n g

the

lens a n d the focusing device w e r e b o t h

things

be-

attached to a metal plate that h a d

n e a t h his microscope.

a

h o l e i n it, j u s t b e l o w t h e l e n s . B y p l a c -

van

Leeuwenhoek

placed

W h e n h e w a s eighty-five, h e discov-

ing objects b e n e a t h the hole, v a n Leeu-

ered

that

"some

hundreds

of

nerves

wenhoek could magnify them as m u c h

e q u a l t h e size of a s i n g l e h a i r of a m a n ' s

a s 3 0 0 t i m e s t h e i r n a t u r a l size.

beard!" A n d when he was past ninety,

H e w a s f a s c i n a t e d b y t h e w o r l d of

he w a s studying "the wonderful perfec-

tiny things that his microscope o p e n e d

t i o n s a n d f o r m a t i o n s " i n t h e e y e of a fly.

u p for him, a n d spent h o u r s examining

W i t h his simple microscope, his care-

a l l s o r t s of t h i n g s a r o u n d h i m a n d w r i t -

ful w o r k , a n d h i s e n t h u s i a s m ,

ing careful reports on w h a t he saw. H e

van Leeuwenhoek opened up a world

p u t m a n y of h i s r e p o r t s i n t o l e t t e r s t h a t

t h a t e v e n t u a l l y l e d t o t h e c o n q u e s t of

h e s e n t t o t h e R o y a l S o c i e t y of L o n d o n ,

m a n y d i s e a s e s a n d a n u n d e r s t a n d i n g of

a n a s s o c i a t i o n m a d e u p of

h o w the m a n y things in t h e w o r l d a r e

The

scientists.

scientists m a r v e l e d at w h a t

van

Antony

constructed.

Leeuwenhoek wrote. They honored him by making their own microscopes a n d imitating his observations. H e h i r e d a n illustrator, called a limner, w h o joined him in his observations

T h e

a n d t h e n m a d e d r a w i n g s of w h a t

M i c r o s c o p e

they

C o m p o u n d

both saw. O n e time van L e e u w e n h o e k p u t a louse u n d e r his microscope. T h i s little a n i m a l w a s t o o active t o o b s e r v e LOUSE

well, so v a n L e e u w e n h o e k r e m o v e d its head. However,

t h e louse's legs

kept

W h e n m o s t people h e a r the w o r d "miWhat is a compound microscope?

croscope," they usually t h i n k of t h e k i n d t h a t is s e e n i n l a b o r a t o r i e s . This

kicking for m o r e t h a n a n h o u r . M e a n -

microscope,

as

in

seen from the outside, h a s a heavy metal

his notes, "the L i m n e r could n o t a d m i r e

foot, a platform o n w h i c h to place w h a t

t h e s i g h t e n o u g h , a n d it t o o k h i m a l o n g

is b e i n g e x a m i n e d ,

time to p u t his h a n d to p a p e r . "

points at the platform, and a long tube

while, as v a n L e e u w e n h o e k w r o t e

GRASS SPIKELET ANTHERS OF FLOWERS

a

nosepiece

that

EYEPE I CE

[ (CONVEX LENS) Part of a feather magnified (below); how light rays pass through a compound microscope (right); a compound microscope (far right) with its parts indicated.

COARSE ADJUSTMENT

L FIRST IMAGE

(CONVEX LENS)

C0NDENSER

SUBSTAGE

NCLINATION JOINT PILLAR

second system can greatly magnify the i m a g e a n d l o c a t e it j u s t a t t h e p l a t f o r m of t h e m i c r o s c o p e .

a t t h e t o p of w h i c h t h e

microscopist

p l a c e s h i s e y e . T h i s k i n d of m i c r o s c o p e is c a l l e d a biological laboratory pound

microscope.

microscope,

or a

I t is a l s o a

com-

Let us examine the compound laboratory microscope in What are some Q r d e r t Q l e a r n i t § . compound microscope?

microscope.

pr a r t s .

First,

examine

let

the

us

part

t h r o u g h w h i c h light passes. R i g h t above the platform, which

In a compound microscope, there are What are the two systems of lenses?

m a n y lenses.

These

i s p r o p e r l y c a l l e d t h e stage,

is a n a r r o w

t u b e t h a t c o n t a i n s l e n s e s . T h i s t u b e is

lenses a r e g r o u p e d in-

c a l l e d t h e objective.

to two systems.

m a y have only one objective that

system

does

One

exactly

what a simple microscope does —

The

into a wider tube, called the

microscope fits

nosepiece.

it

However, most laboratory microscopes

shows an upright image, just as the eye

h a v e two or three objectives attached to

w o u l d s e e it, o n l y l a r g e r . T h e f o c u s of

a rotating nosepiece. W i t h this arrange-

t h i s set of l e n s e s is a t a p o i n t w h e r e t h e

ment, the microscopist need only turn

13

the nosepiece to the right location

in

T h e p a r t s of t h e m i c r o s c o p e y o u h a v e just learned

order to bring into use the objective he wants. Y o u may wonder why a microscope would have more than one

objective.

What are the other parts of a compound microscope?

most

chooses

the objective which magnifies

that

the

important,

but

it w o u l d b e h a r d

to

use them without the o t h e r p a r t s of a m o d -

E a c h objective h a s a different magnifying power. T h e microscopist

are

e r n m i c r o s c o p e . A t t h e b o t t o m of t h e m i c r o s c o p e , is a b r o a d , h e a v y m e t a l

a m o u n t w h i c h best enables h i m to ob-

base,

s o m e t i m e s c a l l e d t h e foot.

s e r v e w h a t h e is l o o k i n g a t . If y o u l o o k

base holds the working

c l o s e l y a t t h e o b j e c t i v e s of a l a b o r a t o r y

microscope

m i c r o s c o p e , y o u will see m a r k e d o n o n e

b a c k of t h e b a s e is t h e pillar.

lOx, on the second 43x, a n d o n the third

holds the microscope steady, but at the

97x. T h e "x" means "times" and stands

t o p of t h e p i l l a r is a j o i n t , t h e

f o r j u s t w h a t it d o e s in m u l t i p l i c a t i o n .

joint,

A n o b j e c t i v e w i t h 4 3 x o n it m e a n s t h a t

m i c r o s c o p e to be tilted b a c k w a r d

and

its lenses will m a g n i f y 4 3 t i m e s n a t u r a l

forward. T h e large curved part

that

size.

d o e s t h e t i l t i n g is c a l l e d t h e arm.

The

steady.

parts

Rising

This of

the

from

the

This, too, inclination

t h a t a l l o w s t h e u p p e r p a r t of t h e

u p p e r e n d of t h e a r m h o l d s t h e t u b e , A b o v e t h e n o s e p i e c e , is a w i d e tube. is u s u a l l y e m p t y , How do you find out the magnifying power of a microscope?

but

sometimes one or two special

lenses

are

within the tube. Fitting i n t o t h e u p p e r p a r t of it is a n a r r o w e r

c a l l e d t h e extension

tube.

tube

T h i s one con-

tains lenses. T h e lenses in t h e portion together make u p the o r ocular.

It

upper eyepiece,

O n t h e o c u l a r , y o u will see its

while the lower end holds the

A f f i x e d t o t h e s t a g e a r e t w o s t r i p s of s p r i n g y s t e e l . T h e y a r e c a l l e d clips,

and

t h e i r t a s k is t o h o l d s p e c i m e n s o n t h e s t a g e , e s p e c i a l l y w h e n t h e s t a g e is t i l t e d . On

more

expensive

microscopes,

the

s t a g e is m a d e i n t w o l a y e r s . T h e u p p e r layer can be moved forward

or back-

w a r d , o r t o t h e r i g h t o r left, b y t u r n i n g p a i r s of k n o b s . W h e r e t h e t u b e m e e t s t h e a r m is a

magnifying p o w e r m a r k e d . Usually, this

very important mechanism —

i s 5 x o r l O x . If y o u u s e a l O x o c u l a r

justment.

with a 43x objective, the

a n d a fine

microscope

stage.

T h e r e is a coarse adjustment.

You

the

ad-

adjustment remember

h a s a t o t a l m a g n i f y i n g p o w e r of 1 0 x 4 3 ,

the screw-threaded rod that van Leeu-

GLOEOCAPSA o r 4 3 0 . I n s h o r t , t o k n o w w h a t t h e m a g n i f y i n g p o w e r of a m i c r o s c o p e is,

w e n h o e k fitted t o h i s s i m p l e m i c r o s c o p e . The

coarse

y o u m u l t i p l y t h e p o w e r of t h e o c u l a r b y

both

t h e p o w e r of t h e o b j e c t i v e .

chined

and the

consist screw

of

fine

very

threads,

adjustments

accurately by

ma-

means

EUGLENA SCENADESMUS

of

which the tubes a n d objectives can be

o n t h e b a l s a m a v e r y t h i n p i e c e of g l a s s ,

raised a n d l o w e r e d , in o r d e r t o

about one inch square, called a

focus

glass

the microscope. A t the very bottom

of t h e a r m ,

a

o r cover

slip.

cover

If y o u s e e b u b b l e s

b e n e a t h t h e c o v e r glass, gently

press

is affixed, s o t h a t a b e a m of l i g h t

d o w n u p o n the cover glass with the tip

can b e shined u p , t h r o u g h a h o l e in t h e

of a p a i r of t w e e z e r s o r a t o o t h p i c k .

s t a g e , t o t h e b o t t o m of t h e

This should help to expel the bubbles.

mirror

objective,

and from there, through the tubes to the eyepiece. B e t w e e n the m i r r o r a n d stage, s o m e m i c r o s c o p e s h a v e a s y s t e m of l e n s e s t o b e t t e r

the third

concentrate

N o w t h e h a i r is p r o p e r l y

mounted.

N e x t , t a k e c a r e of t h e l i g h t i n g .

To

d o this, l o o k a t the stage from t h e side, and with the coarse adjustment,

move

the light from the m i r r o r . T h i s system

t h e b o t t o m of t h e o b j e c t i v e t o a p o i n t

is c a l l e d a substage

a b o u t o n e - s i x t e e n t h of a n i n c h

condenser.

Suppose you wish to examine a from How do you use a laboratory compound microscope?

your

hair

head.

above

t h e c o v e r g l a s s . If t h e m i c r o s c o p e

has

m o r e t h a n one objective, use the

one

with

the

lowest

magnifying

power.

First, place on the

W h e n t h e o b j e c t i v e is p o s i t i o n e d c l o s e

s t a g e a glass

slide,

t o t h e slide, l o o k i n t o t h e eyepiece. W i t h

w h i c h is a p i e c e of

o n e h a n d , m o v e the m i r r o r a b o u t until

clear glass o n e inch

you

see a bright,

evenly-lit

circle

wide a n d three inches long, a n d a b o u t

light, n o t glaring, not dim. N o w

half as t h i c k as w i n d o w glass. P u s h t h e

are r e a d y to focus.

slide u n d e r t h e c l i p s , s o t h a t it is h e l d firmly.

T h e n c u t a o n e - i n c h l e n g t h of

h a i r a n d p l a c e it o n t h e s l i d e r i g h t a b o v e t h e h o l e in t h e s t a g e . Y o u r b r e a t h m i g h t e a s i l y b l o w t h e h a i r a w a y , s o fix it i n p l a c e . T h i s is b e s t d o n e w i t h a m a t e r i a l c a l l e d Canada

balsam.

H o w e v e r , if y o u

h a v e n o b a l s a m , u s e c l e a r h o u s e h o l d cement or clear

fingernail

polish.

P u t a s m a l l d r o p of b a l s a m o n of t h e h a i r . W a i t a f e w m o m e n t s

top in

the h o p e t h a t a n y tiny b u b b l e s in t h e b a l s a m will rise t o t h e s u r f a c e a n d b u r s t . D o n ' t wait t o o long, for C a n a d a b a l s a m (and household cement and

fingernail

polish) h a r d e n in air. So g e n t l y p l a c e ZYGNEMA SYNURA

Preparing a slide for the microscope properly will make viewing easier.

of you

HARVEST MITE GNAT

BURNET BUTTERFLY SWALLOWTAILIL BUTTERFLY

1? ij ?»

EMPEROR MOTH | : i , i

WATER MITE COMMON BLUE BUTTERFLY AZURE BLUE BUTTERFLY

WATER MITE I CABBAGE WHITE BUTTERFLY

RED SPIDER

HAIRSTREAK BUTTERFLY INSECT SCALES

CHEESE MITE

kIT WATER M ITFE

WORM

MITES

DIATOMS

COPEPOD

PROTOZOAN

L

v

MEDUSA JELLYF

OSTRACOD

GASTROTRICHAS

I COPEPOD

DAPHNIA WHITING LARVA V

MARINE PLANKTON CYCLOPS

WATER BEAR nDA HYDRA •

FRESH-WATER PLANKTON

COPEPOD

W h e n f o c u s i n g , y o u m u s t always How d o you , ( . ,

l o w e r p a r t of t h e n o s e p i e c e a r o u n d s o

Always

focus

up-

If y o u f o c u s d o w n w a r d , y o u w i l l front

will n o t o n l y b r e a k t h e s l i d e , a n d p e r h a p s r u i n a v a l u a b l e s p e c i m e n , b u t it m a y a l s o b r e a k t h e f r o n t l e n s of objective. Mindful

of t h i s , t u r n

the slow-

ly t h e c o a r s e a d j u s t m e n t t o w a r d y o u r self, so t h a t t h e t u b e r i s e s f r o m t h e s l i d e . W h e n the hair comes clearly into view, change from the coarse adjustment t h e fine o n e . A l t h o u g h y o u m u s t

to

turn

the c o a r s e a d j u s t m e n t o n l y in o n e direction w h e n focusing, y o u m a y t u r n the

half

a d j u s t m e n t in e i t h e r d i r e c t i o n , as you a turn.

do not

turn

it more

as than

T h u s , w i t h t h e fine a d j u s t -

ment, you can bring the hair into clear f o c u s . Y o u w i l l p r o b a b l y find t h a t y o u have to adjust the mirror again. After you have studied the hair for a w h i l e , y o u m a y w a n t t o m a g n i f y it m o r e .

objectives,

nosepiece

with two

mind this rule: , , Never focus down-

of t h e o b j e c t i v e t h r o u g h t h e s l i d e . T h i s

long

has a

Ar

surely, s o o n e r o r later, p u s h t h e

fine

If t h e m i c r o s c o p e

in

ward. ward.

keep

simply turn

the

t h a t t h e o t h e r o b j e c t i v e is i n l i n e w i t h the

tube.

If

the

microscope

is

well

made, changing the objective should not change the focus very m u c h . However, s o m e f o c u s i n g w i t h t h e fine a d j u s t m e n t will p r o b a b l y b e n e c e s s a r y . A l s o , y o u will h a v e t o a d j u s t t h e l i g h t i n g a g a i n . If t h e m i c r o s c o p e h a s a t h i r d o b j e c t i v e , m o v e it i n t o p l a c e j u s t a s y o u d i d the second one. However, you use this objective simply b y

cannot

focusing.

T h i s objective, usually the one m a r k e d 9 7 x , i s a n oil immersion name because

lens. I t h a s t h i s

t o u s e it, y o u

put the foremost

usually

l e n s of t h e

objec-

t i v e i n t o a d r o p of oil p l a c e d u p o n t h e cover glass. focus,

and

Again

you

will h a v e

this time b e very

because the front

to

careful,

of t h e o b j e c t i v e

is

n e a r l y t o u c h i n g t h e c o v e r glass. T h e oil y o u u s e m u s t b e cedarwood oil c a n b e o b t a i n e d f r o m

oil.

This

microscope

dealers.

If t h e m i c r o s c o p e h a s o n l y o n e n o s e piece, raise t h e objective far a b o v e t h e slide, u n s c r e w t h e o b j e c t i v e t o t a k e it

A f t e r e x a m i n i n g t h e h a i r , y o u will h a v e H o w d o you

to clean the equipment. T u m t h e c o a r s e adjust.

o u t of t h e n o s e p i e c e , a n d t h e n p u t a n other, higher-power, objective into the

' e q u i p m e n tx?0

oil

nosepiece. T h e n focus in t h e s a m e w a y as y o u did w h e n using t h e

low-power

objective. Illustrated on the left are other specimens which may be viewed under the microscope. Mites belong to a family of tiny animals related to spiders and scorpions. They often infest other animals, including humans, plants, and foods. Protozoa, along with other tiny animals, as well as plants, make up the plankton, which floats on the surface of oceans and lakes. Plankton serves as the food for many forms of sea life.

m e n t k n o b to raise the immersion

lens

f r o m t h e slide. T h e n w e t a special k i n d of t i s s u e , c a l l e d lens c a l l e d xylol.

With

tissue, the

in a liquid

wetted

w i p e a l l t h e o i l off t h e o i l lens.

I t is w e l l t o

use

two

tissue,

immersion separate

p i e c e s of t i s s u e f o r t w o w i p i n g s .

The

xylol e v a p o r a t e s quickly, b u t m a y leave a f o g g y d e p o s i t o n t h e l e n s , so w i p e t h e l e n s w i t h a d r y p i e c e of l e n s t i s s u e .

17

If y o u w i s h t o k e e p t h e s l i d e w i t h t h e

m i c r o s c o p e will n o t m a g n i f y m o r e t h a n

m o u n t e d h a i r , w i p e off w i t h x y l o l a n y

1 Ox, a n d t h e v e r y b e s t w i l l m a g n i f y o n l y

excess b a l s a m that has oozed o u t from

20x. In order to really do

u n d e r t h e c o v e r glass, label t h e slide,

w o r k in m i c r o s c o p y , y o u n e e d a com-

a n d s t o r e it. If, o n t h e o t h e r h a n d , y o u

pound

interesting

microscope.

d o n o t w i s h t o k e e p t h e slide m o u n t , p l a c e a d r o p o r t w o of x y l o l

around

A laboratory, or biological, c o m p o u n d microscope

t h e e d g e s of t h e c o v e r g l a s s . T h i s w i l l w o r k i t s w a y u n d e r t h e g l a s s a n d dissolve t h e b a l s a m so t h a t y o u c a n r e m o v e

What kind of microscope should you get?

is w i p e t h e c o v e r g l a s s a n d t h e

slide

very expensive

hundred

d o l l a r s . H o w e v e r , it is p o s s i b l e t o p u r c h a s e a s o - c a l l e d amateur

w i t h s o m e xylol o r lens tissue.

in-

strument that costs several

t h e c o v e r g l a s s . N o w all y o u h a v e t o d o

is a

microscope

w h i c h is m u c h l e s s e x p e n s i v e . T h i s is a If y o u w a n t t o m a k e m i c r o s c o p y y o u r hobby, you What equipment will you need to become a microscopist?

%

will

s m a l l e r m o d e l of t h e l a b o r a t o r y m i c r o scope. It lacks some refinements

have to start with

only

certain

n e e d for his w o r k , b u t in y o u r micros-

basic

equipment:

a

mi-

a

highly-trained

scientist

that

would

c o p y , y o u will n o t miss t h e m a t

all.

glass

T h e s e a m a t e u r microscopes are not toys

slides ( a t least a d o z e n t o begin w i t h ) ;

— they are real c o m p o u n d microscopes

cover glasses ( a b o u t t w o dozen, since

t h a t will p r o d u c e a clear i m a g e magni-

these b r e a k very easily); tweezers

(or

fied 3 0 0 t o 5 0 0 t i m e s . Y o u c a n b u y s u c h

forceps); a medicine dropper; a probe

a m i c r o s c o p e for $ 1 1 to $20. T h i s m a y

(made

croscope;

of

a

s e e m l i k e q u i t e a l o t of m o n e y , b u t if

needle into an eraser removed from

a

you

by

sticking the eye-end

p e n c i l ) ; a sharp knife, or

single-edge

begin

immediately

to put

nickels and dimes that you

find

away you

scissors;

r e a l l y d o n o t h a v e t o s p e n d , y o u will

polish);

have saved u p the needed m o n e y sooner

a n d xylol ( o r a c e t o n e ) . W h i l e a simple

t h a n n o w seems likely. W h e n y o u a r e

m i c r o s c o p e will reveal m a n y

wonders

r e a d y t o b u y y o u r m i c r o s c o p e , y o u will

of t h e w o r l d a r o u n d y o u , t h i s i n s t r u -

b e wise t o c o n s u l t a science t e a c h e r in

m e n t h a s its limits. Y o u c a n n o t b u y o n e

y o u r school. H e c a n give y o u advice o n

t h a t w i l l g i v e t h e 3 0 0 x p o w e r of v a n

h o w to go about buying the microscope.

Leeuwenhoek's.

O n e g o o d p l a c e to b u y a n a m a t e u r mi-

razor

blade;

sharp-pointed

Canada balsam (or

18

Even

fingernail

a

good

simple

SNOW CRYSTALS MAGNIFIED it EEZERS PROBING NEEDLE

c r o s c o p e is f r o m

a mail-order

house.

C o n s u l t its c a t a l o g carefully

before

y o u o r d e r . M a k e s u r e t h e r e is a g u a r a n tee t h a t t h e m i c r o s c o p e will b e r e p l a c e d if it is d e f e c t i v e w h e n y o u g e t it.

T h e

W o r l d

of

Bacteria

a n d

A l l a r o u n d u s a r e b i l l i o n s of t i n y l i v i n g things that are What are the smallest plants • .L 1-10 in the world?

s m a U tQ b e §een

Invisible

Life

P r o t o z o a

B a c t e r i a m a y b e f o u n d all a r o u n d u s — in t h e e a r t h , in w a t e r a n d

too w i t h

, . , , the u n a i d e d eyes. J

—

Where are bacteria found?

in t h e air. T h e r e a r e mill i o n s of b a c t e r i a o n y o u r skin, in y o u r m o u t h , y o u r

A m o n g the smallest

nasal

passages,

and

elsewhere

inside

of t h e s e l i v i n g t h i n g s a r e p l a n t s c a l l e d

y o u r b o d y . T h e r e a r e t h o u s a n d s of dif-

bacteria.

f e r e n t k i n d s of b a c t e r i a . T h e y a r e m a n ' s

A s i n g l e o n e of t h e s e p l a n t s is

a bacterium.

S o m e b a c t e r i a a r e so small

t h a t 1 0 , 0 0 0 of t h e m c o u l d b e p l a c e d o n

invisible friends a n d foes. T h e y a r e b o t h useful a n d harmful to m a n .

t h e p e r i o d a t t h e e n d of t h i s s e n t e n c e . E a c h b a c t e r i u m is a s i n g l e l i v i n g cell.

Among

the useful

T h i s m e a n s t h a t it is a s e p a r a t e b i t of living m a t t e r t h a t c a n live a n d g r o w b y itself. I t c a n t a k e i n t o itself f o o d oxygen. It uses t h e food for

and

nourish-

m e n t , a n d t h e o x y g e n t o h e l p it n o u r i s h

that How are bacteria useful?

bacteria produce

are

those

buttermilk

a n d vinegar, age

cheese,

a n d h e l p i n t h e c u r i n g of leather. Probably the most

v a l u a b l e service t h a t b a c t e r i a give

to

itself, g r o w a n d m o v e . 19

a n d forth rapidly a n d push the bacterium t h r o u g h the liquid. Some bacteria h a v e c i l i a g r o w i n g o u t f r o m a l l p a r t s of t h e cell wall. O t h e r s h a v e just a single t h r e a d a t o n e o r b o t h e n d s . Still o t h e r s h a v e a t u f t of c i l i a a t o n e e n d . Since bacteria are so i m p o r t a n t to m a n , n

When do they thrive best?

it is useful t o k n o w in w h a t c o n d i t i o n s b a c . ,. , t e n a live a n d g r o w .

M o s t bacteria thrive best at the

tem-

p e r a t u r e of t h e h u m a n b o d y — a l i t t l e

Bacilli are rod-shaped bacteria which need oxygen.

m a n is t o c a u s e d e c a y . If d e c a y b a c t e r i a were not constantly at work, the earth would b e c o m e littered with the

dead

b o d i e s of a n i m a l s a n d p l a n t s . Harmful bacteria are those that cause disease in animals a n d plants.

Among

the diseases caused in m a n b y bacteria are p n e u m o n i a , typhoid fever a n d tuberculosis.

Fortunately,

there

are

more

harmless bacteria t h a n harmful ones. B a c t e r i a m a y h a v e a n y o n e of shapes. Some are What do bacteria look like?

like a ball. A

three round

bacterium

of t h i s s h a p e is c a l l e d a coccus.

A n o t h e r k i n d of

Spirilla are threadlike and spiral-shaped bacteria.

b a c t e r i u m is s h a p e d like a r o d , a n d is c a l l e d a bacillus.

T h e t h i r d k i n d of b a c -

less t h a n 9 9 d e g r e e s F a h r e n h e i t .

Both

t e r i u m h a s a s p i r a l s h a p e , a n d is c a l l e d

lower a n d higher temperatures slow the

a

g r o w t h of b a c t e r i a . F r e e z i n g a n d b o i l -

spirillum. they

ing will kill m o s t b a c t e r i a . Y o u c a n n o w

a r e i n a l i q u i d . A b a c t e r i u m of t h i s k i n d

see t h a t p u t t i n g f o o d in t h e refrigerator

has

s l o w s t h e g r o w t h of b a c t e r i a t h a t m a y

Some bacteria can move when extremely

thin

threads

of

living

m a t t e r g r o w i n g o u t f r o m i t s cell w a l l .

be on the food, a n d thereby

T h e s e t h r e a d s , c a l l e d cilia,

the food from b e c o m i n g spoiled. Also,

20

lash

back

prevents

Bacteria reproduce themselves very rapidly. It t a k e s only a b o u t How fast d o t h i r t y m m u t e s f o r o n e bacteria , , _ bacterium to become reproduce? . t w o . If a l l t h e o f f s p r i n g of o n e b a c t e r i u m c o u l d g o o n r e p r o d u c ing for twelve hours, there w o u l d

be

s e v e n t e e n m i l l i o n of t h e m . If t h i s p r o c ess c o n t i n u e d for

five

days,

bacteria

w o u l d fill a l l t h e o c e a n s t o a d e p t h of o n e mile. Of course, n o t h i n g like this can take place, because most bacteria d o n o t find t h e n o u r i s h m e n t o r

favor-

Cocci are ball-like, or spherically-shaped, bacteria.

c o o k i n g f o o d n o t o n l y m a k e s it e a s i e r a n d tastier t o eat, b u t also kills h a r m f u l b a c t e r i a t h a t m a y b e o n it. B a c t e r i a n e e d m u c h m o i s t u r e in o r d e r t o t h r i v e . T h u s , if w e k e e p f o o d

dry,

w e k e e p it f r o m s p o i l i n g b y t h e g r o w t h of b a c t e r i a u p o n it. D a r k n e s s is a n o t h e r condition in w h i c h bacteria thrive.

A

s t r o n g l i g h t w i l l s l o w t h e g r o w t h of b a c teria o r kill t h e m . N o w y o u c a n

see

w h y a s u n n y r o o m is a h e a l t h y r o o m . I n m o s t c i v i l i z e d c o u n t r i e s , t h e l a w requires that What is the process of pasteurization?

bacteria

in milk b e killed b y raising the temperat u r e of t h e m i l k

Cocci may also grow in pairs, clusters or in chains.

to

1 4 5 d e g r e e s F a h r e n h e i t a n d k e e p i n g it

a b l e c o n d i t i o n s in w h i c h t o g r o w

at this t e m p e r a t u r e for thirty minutes.

reproduce.

and

T h i s p r o c e s s f o r k i l l i n g b a c t e r i a is c a l l e d pasteurization

and was discovered

the great F r e n c h bacteriologist

by

O n e of t h e b e s t w a y s t o g e t h a r m l e s s

Louis

b a c t e r i a is t o m a k e a hay infus[orii pjH a two-quart

P a s t e u r . A b a c t e r i o l o g i s t is a s c i e n t i s t

How c a n

w h o studies a n d w o r k s with bacteria —

. . , bacteria?

o r t h e s c i e n c e of b a c t e r i o l o g y .

g l a s s j a r a l m o s t full of w a t e r . If y o u c a n g e t w a t e r 21

9:00 A.M.

from a stream or lake, you can proceed

c a r e f u l l y a n d a d j u s t t h e m i r r o r i n sev-

i m m e d i a t e l y w i t h t h e r e s t of t h e e x p e r i -

eral different positions as y o u seek for

m e n t . If y o u t a k e w a t e r f r o m

b a c t e r i a i n t h e field of y o u r m i c r o s c o p e .

a

tap,

If y o u s e e n o t h i n g b u t a b l u r r y

blob

t h r e e d a y s , s o t h a t e x c e s s o x y g e n t h a t is

of

have

p r o b a b l y dissolved in the water

may

p l a c e d t o o l a r g e a n a m o u n t of s c u m o n

e s c a p e . P a s t e a l a b e l o n t h e o u t s i d e of

t h e slide. M a k e a n e w slide, u s i n g o n l y

t h e j a r a t t h e l e v e l of t h e s u r f a c e of t h e

one-tenth as m u c h scum. In trying to

w a t e r , so t h a t y o u m a y a d d m o r e w a t e r

find b a c t e r i a , t h e l i g h t i n g is v e r y i m p o r -

t o t h e j a r , if n e e d e d . A d d o n l y w a t e r

t a n t . S p e n d c o n s i d e r a b l e t i m e in m a n i p -

that y o u h a v e allowed to stand for

u l a t i n g t h e m i r r o r . I n y o u r r e p o r t , de-

allow the jar to stand uncovered

GfiXfe 1

10:00 A.M.

9:40 A.M.

9:20 A.M.

Many bacteria reproduce by splitting in two — a half hour process. Some split in 20 min.

for

a

C u t a h a n d f u l of h a y o r d r y

it m e a n s

that you

s c r i b e t h e s h a p e s of t h e b a c t e r i a

while, like t h e original jar. 2

material,

grass

i n t o s h o r t l e n g t h s a n d p u t it i n t o

the

you

see. T h e r e a r e m a n y o t h e r s o u r c e s of b a c -

w a t e r in the jar. C o v e r t h e j a r a n d p l a c e

teria a m o n g

it w h e r e d a y l i g h t , b u t n o t d i r e c t

L e e u w e n h o e k by scraping with a tooth-

sun-

everyday things.

Imitate

l i g h t , w i l l r e a c h it. I n a b o u t t h r e e o r f o u r d a y s , y o u will n o t i c e a s c u m

on

An organism continues to reproduce in a new culture.

t h e s u r f a c e of t h e w a t e r a n d a n a c c o m p a n y i n g u n p l e a s a n t o d o r . T h e s c u m is f o r m e d b y b i l l i o n s of b a c t e r i a .

REMOVE DROPLETS FROM HAY INFUSION AND PLACE ON SLIDE

P l u n g e t h e t i p of y o u r m e d i c i n e d r o p p e r beneath the scum, and How do you prepare bacteria for the microscope?

| i \ V

d r a w u p some clear wat e r . P l a c e a d r o p of t h i s w a t e r o n a glass slide. Using your probe, pick

\ h

u p a very small a m o u n t of s c u m —

just e n o u g h to cover

the

p o i n t of t h e n e e d l e — a n d d i p t h e n e e d l e into the drop k

of w a t e r o n t h e

t

PICK UP ORGANISM WITH DROPPER AND PLACE IN NEW CULTURE MEDIUM

slide.

Place a cover glass over the drop. F o c u s I

(1) Streptococci. (2) Sfaphy/occi. (3) Tetanus bacilli. (4) Typhoid bacilli. (5) Tuberculosis bacilli. (6) Cholera vibrio. All are disease-causing bacteria in man. 22

p i c k a t i n y b i t of t h e w h i t e

material

from y o u r teeth, just at the gum-line.

preparing

bacteria

that

makes

them

m u c h e a s i e r t o see.

P l a c e t h i s w h i t e m a t e r i a l i n a d r o p of w a t e r , o n a slide. M a k e a few c u t s in a

Y o u c a n p r e p a r e a s l i d e of b a c t e r i a s o that

p e a c h o r a n a p p l e , a n d let t h e fruit s t a n d in a w a r m , d a m p p l a c e for a few d a y s . P l a c e a b i t of t h e m a t e r i a l f r o m t h e c u t

How can

§een^

you s a m bacteria?

^ ^

i n a d r o p of w a t e r o n a s l i d e , a n d e x a m i n e it f o r b a c t e r i a . M i x a p i n c h of soil in a l i t t l e w a t e r . P l a c e a d r o p of t h i s m i x t u r e o n a s l i d e a n d e x a m i n e it f o r bacteria.

they will b e •£ y Q U sfa^n ^

easily ^ac_

Q\faeT

blue.

recj

o r

F i r s t , of c o u r s e , y o u w i l l n e e d t h e s t a i n . T h e b l u e s t a i n is c a l l e d methylene eosin.

blue,

and the red

stain

is

Y o u c a n b u y b o t h of t h e m f r o m

a pharmacist. They are cheap, and you

P l a c i n g b a c t e r i a i n a d r o p of w a t e r

n e e d v e r y l i t t l e of e a c h . If y o u b u y t h e

o n a slide m a k e s a p r e p a r a t i o n t h a t re-

s t a i n s in d r y f o r m , d i s s o l v e i n h a l f

q u i r e s m u c h m a n i p u l a t i o n of t h e m i r r o r

tumblerful

in o r d e r t o b e a b l e t o s e e t h e b a c t e r i a

e i t h e r a s y o u c a n p i c k u p o n t h e e n d of

at all. T h i s m e t h o d h a s t h e a d v a n t a g e

a knife b l a d e . T h i s will give y o u e n o u g h

o f . p r e s e n t i n g for e x a m i n a t i o n live bac-

t o l a s t f o r m o n t h s . I t is w i s e t o k e e p

t e r i a , s o m e of w h i c h m a y b e

t h e stains in s t o p p e r e d bottles, so t h a t

moving.

T h e r e is, h o w e v e r , a n o t h e r m e t h o d of

of w a t e r j u s t a s m u c h

a of

the water does not evaporate.

Many microorganisms flourish in a hay infusion. Shown are the co/poda, hay bacillus, and vo/vox, all magnified.

If y o u c a n n o t b u y t h e s e t w o s t a i n s ,

ter, a n d spread the m i x t u r e into a b r o a d

you can use ink. F o r the blue stain use

s m e a r . G r a s p t h e slide b y the edges n e a r

t h e " p e r m a n e n t " k i n d of b l u e f o u n t a i n

one

pen ink, which contains methylene blue.

above a candle

F o r r e d s t a i n u s e a n y k i n d of r e d i n k .

e v a p o r a t e s . H o l d t h e slide

end,

and

hold

it

flame

several

inches

until the

water

sufficiently

h i g h a b o v e t h e flame s o t h a t t h e w a t e r P r e p a r e t h e stained slide in this m a n n e r : P l a c e a d r o p of w a t e r & d e a n s H d e Ug_ , , , m o u r r o b e a d d a ^ y P ' s m a l l a m o u n t of t h e

H o w can you prepare a s t a i n e d slide?

Q n

bacteria-containing material to the wa-

does n o t boil. Y o u d o n o t w a n t to cook the bacteria. W h e n a l l of t h e w a t e r h a s e v a p o r a t e d a n d t h e s l i d e is t h o r o u g h l y d r y , p a s s t h e slide t h r o u g h t h e c a n d l e

rapidly

t h r e e o r f o u r t i m e s . T h i s a c t i o n is c a l l e d fixing

Picture-instructions for preparing a stained slide:

flame

the smear.

When

the

slide

has

cooled

thor-

oughly, d r o p a stain from your medicine d r o p p e r o n t h e fixed s m e a r . S o m e b a c teria i> 2. HOLD HIGH ABOVE FLAME TO EVAPORATE WATER

stain better

with blue dye

and

others stain better with red dye.

You

will h a v e t o e x p e r i m e n t w i t h b o t h colors t o s e e w h i c h o n e b e s t s t a i n s t h e k i n d of

1. PLACE MATERIAL ON SMEAR OF WATER

bacteria you are working with. Leave

^

stain on

the smear

for

a b o u t a m i n u t e . S o m e b a c t e r i a will n e e d

C M )

\

the

m o r e t h a n a m i n u t e to stain thoroughly. A g a i n , y o u will h a v e t o l e a r n this b y experience. After the stain has been on t h e s m e a r f o r t h e p r o p e r l e n g t h of t i m e ,

PASS SLIDE THROUGH FLAME THREE TIMES TO "FIX" SMEAR 4. ADD STAIN TO SMEAR

wash

i t off

with running

tap

water.

T h e n , p l a c e t h e slide, s m e a r - s i d e u p , o n a p a p e r towel. F o l d the towel over and b l o t t h e slide carefully. D o n o t r u b t h e towel o n t h e s m e a r . T h i s will destroy t h e s m e a r . N o w , e x a m i n e t h e slide un-

\ 5. WASH OFF EXCESS STAIN

der the microscope. T h e r e is a n o t h e r w a y t o p r e p a r e a s l i d e a t is a demount?

6. BLOT DRY

fi

1

of b a c t e r i a , s o t h a t yOU c a n 0 b s e r v e thern a l i v e . T h i s is c a l l e d t h e hanging drop m e t h o d .

T h e r e is a k i n d of t h i c k g l a s s s l i d e t h a t

h a s a little well g r o u n d i n t o its center. T h i s slide is u s e d t o set u p a h a n g i n g drop

mount.

Such

slides a r e

1. LINE RIM OF COVER SLIP WITH VASELINE

expen-

sive, so y o u w o u l d p r o b a b l y d o

best

if y o u m a k e y o u r o w n h a n g i n g

drop

2. ADD DROP OF CULTURE TO CENTER

apparatus. C u t a p i e c e of c a r d b o a r d e x a c t l y s i z e of a g l a s s How can you make your own hanging drop mount?

the

slide.

Y o u can d o this best by tracing the outline of t h e s l i d e o n

the

cardboard.

cut

Now,

^

W

,

BUILD A WELL OUT OF THREE CARDBOARD WASHERS

the cardboard into three equal lengths. W i t h y o u r p o i n t e d scissors, c u t a hole, n o bigger t h a n half a n inch, in t h e cent e r of e a c h of t h e t h r e e p i e c e s of c a r d board. G l u e the three pieces together,

4. TURN UPSIDE DOWN AND PLACE AGAINST COVER SLIP

o n e o n t o p of t h e o t h e r , s o t h a t t h e r e i s a single h o l e t h r o u g h all t h r e e . C e m e n t this c a r d b o a r d " w a s h e r " to the

center

of a g l a s s s l i d e . C o v e r o n e of y o u r

5. TURN RIGHT SIDE UP QUICKLY

finU = i ^ t = j

gers lightly w i t h p e t r o l e u m jelly — like Vaseline. H o l d i n g a cover glass in y o u r h a n d , s c r a p e t h e j e l l y off y o u r

SIDE VIEW OF SLIDE, WELL, HANGING DROP

finger,

u s i n g a l l t h e e d g e s of t h e c o v e r g l a s s , u n t i l t h e r e is a r i m of j e l l y a l l a r o u n d t h e e d g e s of t h e c o v e r g l a s s . P l a c e t h e

Picture-directions for preparing hanging drop mount.

glass o n t h e table, jelly-side u p . U s i n g y o u r p r o b e , p l a c e a m i x t u r e of a n d a d r o p of t h e

water

bacteria-containing

material you want to examine on

the

will b e h a n g i n g d o w n f r o m t h e

cover

glass. E x a m i n e t h e d r o p u n d e r t h e mic r o s c o p e , f o c u s i n g it c a r e f u l l y .

c e n t e r of t h e c o v e r g l a s s . H o l d t h e glass slide so t h a t t h e c a r d board washer

is u n d e r n e a t h

and

Perhaps, when you were looking at bacteria from

the

h o l e i n t h e w a s h e r is r i g h t o v e r t h e cent e r of t h e c o v e r g l a s s . L o w e r t h e s l i d e ,

What are the smallest animals in the world?

r i m of t h e c o v e r g l a s s . T h e n , w i t h

a

field

quick m o t i o n , t u r n t h e slide over.

A

one-celled

you

saw a large object swim across

a n d p r e s s t h e w a s h e r firmly o n t h e j e l l y

d r o p of t h e m i x t u r e y o u a r e t o e x a m i n e

h a y infusion,

your

your

of v i e w . T h i s l a r g e o b j e c t w a s a

protozoa.

animal

of

This name

the kind means

called

"earliest

25

•»K__i

easier

to

find

protozoa

and

a

little

h a r d e r to find bacteria. Also,

the

a m o u n t of s c u m s e e m e d t o l e s s e n . T h i s was because the protozoa were feeding o n t h e b a c t e r i a . T h e y i n c r e a s e d in n u m ber as they ate u p the bacteria. Protozoa

are

interesting

to

watch

under a microscope because they have so m a n y different f o r m s a n d t h e y m o v e a b o u t in m a n y different ways. Y o u c a n see t h e m

hunting

and

catching

their

f o o d , w h i c h is u s u a l l y b a c t e r i a , b u t m a y

The whips of flagellated bacteria help them to swim.

Foul water teems with harmful disease-causing bacteria. f o r m of a n i m a l s " a n d r e f e r s t o t h e f a c t that protozoa were probably the

first

CHRYSAMOEBA

a n i m a l s t o a p p e a r i n t h e o c e a n s of t h e

GONYAULAX

e a r t h h u n d r e d s of m i l l i o n s of y e a r s a g o . T h e y a r e still w a t e r a n i m a l s , a n d f o u n d in t h e seas, lakes a n d

are

streams.

A s i n g l e o n e of t h e s e a n i m a l s i s c a l l e d a

b e j u s t b i t s of o n c e - l i v i n g p l a n t o r a n i mal material

floating

a b o u t in the water

— o r it m a y b e o t h e r p r o t o z o a .

protozoan. A p r o t o z o a n , l i k e a b a c t e r i u m , is a

s e p a r a t e b i t of l i v i n g m a t t e r t h a t

T h e h a n g i n g d r o p m e t h o d is o n e of t h e

can

t a k e i n a n d u s e f o o d , g e t r i d of w a s t e s , move, grow and reproduce. There are t h o u s a n d s of k i n d s . M o s t a r e h a r m l e s s ,

b e s t w a y s of p r e p a r i n g How can you examine protozoa?

a slide for t h e examin a t i o n of The

main

protozoa. difficulty

b u t a few are harmful to m a n . A m o n g

w i t h t h i s m e t h o d is t h a t t h e d r o p p r o -

the harmful ones are those that

cause

vides the tiny animals with such a large

such diseases as malaria, dysentery a n d

ocean to swim in that they swim either

sleeping sickness.

a b o v e o r b e l o w t h e level o n w h i c h y o u r m i c r o s c o p e is f o c u s e d . O n e b i g a d v a n -

If y o u w o r k e d w i t h y o u r h a y What do the protozoa eat?

26

infusion

t a g e of t h e h a n g i n g d r o p m o u n t f o r p r o -

for several days, you

t o z o a is t h a t t h e w a t e r d o e s n o t e v a p o -

may have noticed that

r a t e easily, a n d y o u c a n w a t c h t h e tiny

it b e c a m e c o n t i n u a l l y

animals for a long time.

A n o t h e r w a y t o p r e p a r e a slide for

O n e w a y to k e e p the protozoa in place

t h e o b s e r v a t i o n of p r o t o z o a is s i m p l y

is t o t r a p t h e m i n t h e fibers of a p i e c e

t o p l a c e a d r o p of w a t e r f r o m a h a y

of t h r e a d .

i n f u s i o n o n a g l a s s s l i d e a n d c o v e r it

t h r e a d so t h a t the

gently w i t h a cover glass. W h e n obtain-

Flatten

ing the drop, p o k e y o u r medicine drop-

d r o p of w a t e r o n t h e s l i d e , b e f o r e y o u

p e r b e n e a t h t h e s c u m o n t h e s u r f a c e of

p u t o n t h e cover glass. T h e

the infusion.

form

T h e cover glass

flattens

t h e d r o p of

w a t e r so m u c h t h a t t h e r e is v e r y little

a

Fray

a half-inch fibers

piece

of

make a mat.

t h i s m a t , a n d p l a c e it i n

the

fibers

will

" n e t " t h a t will e n t a n g l e

and

hold, or slow d o w n , the p r o t o z o a in the water.

r o o m for the p r o t o z o a to swim u p a n d down. Once you have focused on one

You

may

see o n e or m o r e

of t h e m , i t w i l l u s u a l l y r e m a i n i n f o c u s for a long time. T h e m a i n d i s a d v a n t a g e of t h i s m e t h o d of m o u n t i n g is t h a t t h e water evaporates quite rapidly.

While

you are looking at a particularly interesting p r o t o z o a n , the slide m a y d r y u p right u n d e r y o u r eyes. Y o u c a n p r e v e n t this from h a p p e n i n g b y p u t t i n g a r i m of p e t r o l e u m j e l l y a r o u n d t h e e d g e s of

How do protozoa , ._ move about?

protozoa

move around under y Q u r microscope, and, , . unless y o u k n o w lust , , , w h a t t o l o o k for, y o u

m a y b e u n a b l e t o tell j u s t h o w

they

move. Some protozoa move through the w a t e r b y m e a n s of c i l i a a l o n g t h e s i d e s of t h e i r b o d i e s . S o m e p r o t o z o a n s h a v e a t o n e e n d a t h r e a d of l i v i n g

matter

t h a t is l o n g e r a n d t h i c k e r t h a n a c i l i u m . Ciliated bacteria have fringed hairs which vibrate.

T h i s t h r e a d is c a l l e d a

flagellum,

a Latin

The tsetse fly carries the parasite (left) of human sleepng sickness.

DIDIDIUM STYLONICHIA t h e c o v e r g l a s s , after

it is p l a c e d u p o n

t h e d r o p of w a t e r . Y o u w i l l find t h a t m a n y p r o t o z o a

are

simply t o o active t o enHow can you keep protozoa in place?

able you to get a look at them,

especially

when you are using high-power

good the

objective.

The anopheles mosquito, which carries the malaria parasite (right), transmits malaria.

word that means "whip." Some proto-

a half d o z e n r a g g e d projections

zoa pull themselves through the water

ing out from

by beating these whips d o w n to their

body.

stick-

t h e c e n t r a l m a s s of

its

sides. O t h e r s use t h e w h i p as a tail a n d p u s h themselves t h r o u g h t h e w a t e r in

Y o u m u s t w a t c h a n a m o e b a for s o m e

the same way you can push a small boat along b y m o v i n g a single o a r b a c k a n d forth

in t h e w a t e r b e h i n d

the

boat's

stern.

How does an amoeba move?

t i m e in o r d e r to see h o w it m o v e s . I n t h e first p l a c e , i t s p e n d s

a g r e a t p a r t of its t i m e resting, or, a t least, n o t moving. Secondly, an a m o e b a that

m o v e s very slowly. A s y o u w a t c h , you

y o u a r e l i k e l y t o find i n , . - . a h a y i n f u s i o n is o n e *

w i l l s e e t h a t a p r o j e c t i o n of l i v i n g m a t e -

called

is c a l l e d a pseudopod,

T h e only whip-bearing protozoan W h a t is a _ . Peranema?

Peranema.

You

rial slowly m o v e s

outward

from

the

m a i n p a r t of i t s b o d y . T h i s p r o j e c t i o n o r false

foot.

will r e c o g n i z e this o n e b e c a u s e it h a s

T h e n , y o u will see m o r e living

two whips, a long one a n d a short one,

rial s t r e a m i n g i n t o t h e false foot, w h i c h

a t o p p o s i t e e n d s of t h e b o d y . Y o u m a y

will

be puzzled to understand what

the amoeba

Peranema

makes

m o v e , w h e n its w h i p s s e e m

grow

larger.

Eventually,

will h a v e

mateall

streamed

of into

what was a pseudopod, and the whole

t o b e s t a n d i n g still. If y o u l o o k c l o s e l y

a m o e b a will n o w b e at t h e p l a c e

a t t h e t i p of t h e l o n g o n e , y o u w i l l s e e

w h i c h t h e p s e u d o p o d first r e a c h e d o u t .

that

it

is

vibrating

back

and

v e r y r a p i d l y . A l s o , Peranema

forth

is a l w a y s

c h a n g i n g s h a p e . S o m e t i m e s it l o o k s like a radish, sometimes like a bulging pot a t o . T o s e e Peranema

well, y o u m u s t

use a high-power objective a n d a rather d i m light. If

you

scrape

the

inside

of

to

your

mouth with a toothpick and make

a

s l i d e of t h e m a t e r i a l o b t a i n e d , y o u m a y b e a b l e t o see o t h e r w h i p - b e a r e r s . Seve r a l k i n d s live in t h e h u m a n b o d y , a n d a l m o s t a l l of t h e m a r e e n t i r e l y h a r m l e s s .

O n e of t h e m o s t c o m m o n k i n d of p r o t o z o a is a paramecium. What is a I t is s h a p e d s o m e t h i n g Paramecium? like a long slipper. Its b o d y is c o v e r e d w i t h c i l i a t h a t b e a t b a c k a n d forth very rapidly. Since there are h u n d r e d s of c i l i a o n t h e b o d y , a n d a l l are acting like tiny oars, the p a r a m e c i u m is m o v e d t h r o u g h t h e w a t e r v e r y r a p i d l y . A p a r a m e c i u m is a l s o o n e of t h e l a r g e s t of t h e p r o t o z o a . I t m a y r e a c h a d i a m e t e r of m o r e t h a n 1 / 1 0 0 of a n

Y o u r h a y infusion m a y yield a m o r e or

i n c h . If y o u s e e o n e u n d e r y o u r m i c r o -

less shapeless p r o t o z o a n

scope, it m i g h t b e i n t e r e s t i n g t o r e m o v e

c a l l e d a n amoeba.

This

t h e slide f r o m t h e clips a n d see w h e t h e r

protozoan has n o partic-

y o u c a n see t h e p a r a m e c i u m w i t h y o u r

u l a r s h a p e . S o m e t i m e s it m a y b e n e a r l y

n a k e d eye. T o d o this p l a c e t h e slide o n

r o u n d , a n d a t o t h e r t i m e s it m a y h a v e

a b l a c k b a c k g r o u n d , a n d shine a light

What is an amoeba?

28

directly d o w n u p o n t h e cover glass. T h e p a r a m e c i a will b e seen a s b r i g h t m o v i n g specks. Protozoa,

such

as

What is inside a protozoan?

the

amoeba

and

paramecia, are large enough not

so

only

that

can

we

study

their general form, b u t w e c a n e x a m i n e w h a t is inside t h e m . S i n c e e a c h p r o t o z o a n is a s i n g l e livi n g cell, i t p o s s e s s e s s o m e o f t h e c h a r a c t e r i s t i c s of

a l l l i v i n g c e l l s . I t is

sur-

r o u n d e d b y a m e m b r a n e t h a t h o l d s it together.

The

living m a t e r i a l

that

w i t h i n t h e cell m e m b r a n e is c a l l e d plasm.

If y o u e x a m i n e t h e

carefully,

you

will

see

is

cyto-

cytoplasm

that

it

looks

g r a i n y , a s if it w e r e m a d e u p of g r a i n s of c o l o r l e s s s a n d . I t i s t h i s g r a i n i n e s s that

enables

the

cytoplasm

in

the

a m o e b a t o s t r e a m i n t o its false

feet,

just as s a n d in a sack c a n b e m a d e t o flow a r o u n d b y m o v i n g t h e s a c k . W i t h i n t h e c y t o p l a s m is a l a r g e d a r k d o t . T h i s i s t h e c e l l ' s nucleus.

All the

m o v e m e n t s a n d a c t i v i t i e s of t h e p r o t o z o a n a r e d i r e c t e d b y it. I t is s o m e w h a t as t h o u g h the nucleus w e r e the

cell's

brain. Somewhere

in

the

cytoplasm

of

an

a m o e b a or a ParaHow do protozoa collect wastes and water?

mecium, you

will

see o n e o r t w o ( o r m o r e ) large

clear

circles. I n t h e p a r a m e c i u m , y o u

may

Peranema changes shape by contracting, expanding.

29

see a clear, s t a r - s h a p e d spot. T h e s e a r e

m e m b r a n e b e t w e e n t h e m dissolves, a n d

contractile

t h e f o o d p a r t i c l e is i n s i d e t h e a m o e b a .

vacuoles.

They move about

within the cytoplasm collecting

waste

materials a n d excess water. W h e n they

A p a r a m e c i u m h a s a t o u g h e r cell m e m -

r e a c h t h e m e m b r a n e of t h e p r o t o z o a n ,

very

brane, and cannot, therefore, p u t out pseu, , , d o pr o d s t o s u r r o u n d a . b i t of f o o d . I n s t e a d , t h e

small, b u t as it m o v e s a b o u t p i c k i n g u p

P a r a m e c i u m h a s a m o u t h a n d a gullet

waste materials

i n t o w h i c h n o u r i s h m e n t is t a k e n . If y o u

they suddenly contract a n d expel their b u r d e n o u t s i d e t h e cell wall. A f t e r this happens,

the

vacuole and

becomes water,

it

grows

larger.

How does a paramecium » •» t M g e t its food?

l o o k closely a t a p a r a m e c i u m , y o u will see a g r o o v e a l o n g o n e side, n e a r t h e

Also

within

the cytoplasm,

How does the amoeba eat?

you

p r o b a b l y see

will small

d a r k dots with lighter circles a r o u n d

them.

T h e s e a r e b i t s of f o o d t h a t t h e p r o t o -

f r o n t e n d . T h i s is t h e oral groove.

Focus

very carefully, a n d y o u m a y be able to s e e t h a t t h e o r a l g r o o v e is l i n e d w i t h cilia. W h e n a p a r a m e c i u m c o m e s u p o n food

particles,

usually

bacteria,

the

b e a t i n g of t h e c i l i a s h o v e t h e p a r t i c l e s CYTOPLASM SSSSSk/ * f t / ^W PSEUDOPOD

k

J

NUCLEUS / k

CELL

£

'~*'•••'irk

along the oral groove to a point near

MEMBRANE r

t h e m i d d l e of t h e b o d y w h e r e t h e r e is a t u b e . T h e o p e n i n g of t h i s t u b e is t h e

/

' " " - ^

mouth,

a n d t h e t u b e , i t s e l f , is t h e

gullet.

When

food particles reach the

lower

e n d of t h e g u l l e t , t h e y c o l l e c t i n t o a ball, a n d this ball, a l o n g w i t h a little

4

water, : %

VP

floats

into the cytoplasm.

You

see t h e f o o d as a d a r k d o t , a n d t h e w a t e r M \

i

i i FOOD PARTICLE

-

^

as the light circle a r o u n d the dot. T o g e t h e r , t h e y m a k e u p a food

vacuole.

S i n c e t h e f e e d i n g a c t i o n s of

protozoa

CONTRACTILE VACUOLE

The amoeba is a microscopic, single-celled animal. Its name comes from the Greek word for change.

H o w can you feed protozoa?

are so you

interesting,

may

want

to

p r o v i d e f o o d in orz o a n h a s t a k e n i n t o itself, a n d i t is i n t e r -

d e r t o w a t c h t h e m t a k e it i n t o t h e i r b o d -

e s t i n g t o w a t c h h o w t h i s is d o n e . W h e n

ies. P i c k off f r o m a c a k e of y e a s t a p i e c e

a n a m o e b a c o m e s u p o n a b i t of f o o d ,

a b o u t t h e size of t h e e y e of a n e e d l e .

it r e a c h e s o u t t w o p s e u d o p o d s t o sur-

M a s h t h e s p e c k of y e a s t i n a d r o p of

r o u n d the food particle. W h e n the pseu-

w a t e r . P l a c e a l i t t l e of t h i s m i x t u r e i n

dopods have curved completely around

t h e c e n t e r of a d r o p of w a t e r t h a t c o n -

t h e p i e c e of f o o d , t h e y m e e t . T h e n t h e

t a i n s p r o t o z o a . P l a c e a c o v e r slip o n t h e

30

The illustrations show how the pseudopods of an amoeba engulf a particle of food, until the food is completely inside the protozoan.

w a t e r . D i p t h e e n d of a t o o t h p i c k i n t o

fore it e n c o u n t e r e d u n f a v o r a b l e

r e d i n k a n d t r a n s f e r a s m a l l d r o p of i n k

tions.

condi-

t o t h e e d g e of t h e c o v e r g l a s s . T h e r e d d y e in t h e i n k will m a k e it easier for

Since t h e grass y o u used for m a k i n g a hay

y o u t o see t h e f o o d - t a k i n g a c t i v i t i e s . W h e n bacteria or protozoa

find

them-

selves in c o n d i t i o n s H o W

d0

baCteria

i and protozoa suspend life?

t h a t

they

a r e

° dl7, temporarily

Where do hayinfusion bacteria and protozoa come from?

processes, without actually dying. a c c o m p l i s h this, they s u r r o u n d

To

them-

dry, you m a y wonder

where

living

water-

creatures and

p r o t o z o a c a m e from after the grass h a d soaked for a few days. Bacteria

and

p r o t o z o a t h a t h a d been living o n

the

h a y - i n f u s i o n g r a s s b e f o r e it d r i e d f o r m e d

selves w i t h a v e r y t o u g h c o v e r i n g t h a t

spores and

protects them from completely

place. W h e n

drying

was

like bacteria

t o

suspend their living

infusion

cysts w h e n

drying

took

y o u p l a c e d t h e g r a s s in

out, a n d also from s u d d e n c h a n g e s in

w a t e r , t h e w a l l s of t h e s p o r e s a n d c y s t s

t e m p e r a t u r e . A b a c t e r i a in this condi-

dissolved.

t i o n is c a l l e d a spore, is a cyst.

and a protozoan

Spores a n d cysts are very light

A few days after you p u t the dry grass into the water,

a n d c a n b e easily c a r r i e d b y even t h e lightest breezes. W h e n a spore or cyst a g a i n h a p p e n s upon wet conditions, the thick covering

How do trie number of bacteria and protozoa increase?

a

scum

u p of

made

bacteria

appeared

in

dissolves a n d the b a c t e r i u m or the pro-

y o u r h a y infusion. F o r a few days, the

t o z o a n g o e s o n l i v i n g j u s t a s it d i d b e -

a m o u n t of s c u m i n c r e a s e d ,

thereby

31

I

The common bread mold, Rhizopus nigricans, irequently grows on old bread, and is magnified above

Molds,

Mildew,

S p r i n k l e w a t e r o n f o u r o r five s l i c e s of How can you grow plants on a slice of bread?

Yeast

B u d d i n g

terial p e p p e r e d with black dots.

This

bread. Wipe the d a m p

m a t e r i a l is t h e t h i c k g r o w t h of a p l a n t

side

c a l l e d common

of

these

across the

slices

floor,

tak-

bread

mold.

T o e x a m i n e this m o l d , place a small

ing care not to crum-

p i e c e of b r e a d o n t h e s t a g e of

ble the bread. P u t the

m i c r o s c o p e . Shine a bright light d o w n

b r e a d into a closet o r s o m e o t h e r w a r m ,

o n the m o l d . B e sure t h a t the light does

dark place. T w o days later,

n o t a l s o s h i n e in, y o u r e y e s a n d h i n d e r

t h e slices. Y o u w i l l p r o b a b l y

examine find

on

t h e m p a t c h e s of a w h i t e c o t t o n y m a 34

your

y o u r viewing. U s e the low-power objective to e x a m i n e the b r e a d m o l d .

N o t e t h a t t h e w h i t e c o t t o n y m a t e r i a l is What do molds look like?

a

tangled

mass

the

of

b r e a d b y m e a n s of t h e l o w - p o w e r o b -

is

jective, e x a m i n e it in a different

filaments.

This

called

mycelium.

a

Having examined the mold on

way.

S c r a p e s o m e m o l d off t h e b r e a d

and

T h e t h r e a d l i k e g r o w t h s a r e m a d e of liv-

p l a c e i t o n a g l a s s s l i d e . A d d a d r o p of

i n g m a t t e r . T r a c e o n e of t h e

filaments.

w a t e r a n d a d r o p of a l c o h o l . T h e n c o v e r

horizontally

it w i t h a c o v e r glass. L i g h t t h e slide in

f o r a s h o r t d i s t a n c e , t h e n it b r a n c h e s

t h e u s u a l w a y ; t h a t is, b y m e a n s of l i g h t

into several vertical filaments. O n

reflected u p w a r d from the

Y o u will see t h a t it r u n s

the

microscope

t o p of e a c h of t h e s e v e r t i c a l g r o w t h s is

mirror. First examine the mold with the

a b l a c k k n o b . T h e s e a r e sporangia,

or

low-power objective. T h e n use the high-

W i t h i n e a c h o n e of t h e s e

p o w e r objective. Y o u will see t h a t e a c h

spore

cases.

cases are a large n u m b e r

of

spores.

m o l d p l a n t is m a d e of m a n y cells. Y o u

burst

m i g h t e v e n b e a b l e t o see a n u c l e u s in

S o o n e r o r later, t h e k n o b s will

o p e n . T h e spores a r e so light t h a t t h e y w i l l e a s i l y float a w a y i n t h e a i r . W h e n a spore alights on some material the m o l d c a n use for food, t h e

that spore

o n e of t h e s e cells. I t i s p o s s i b l e t h a t a l o n g w i t h , o r ins t e a d of, c o m m o n b r e a d m o l d , y o u will find

an orange, black, green, or

pink

will g r o w i n t o a w h o l e n e w m o l d p l a n t .

mold

It was spores wiped u p from the

c o l o r r e p r e s e n t s a d i f f e r e n t s p e c i e s of

floor

that grew into mold on your bread. Directly

beneath

the

vertical

filaments

fila-

nourishment the mold plant needs

in

o r d e r to live a n d g r o w . Most molds are harmless to man, though few

may

diseases.

cause

One

d i s e a s e is

Each a

c o m p a r i s o n of t h e s h a p e s a n d c o l o r s of t h e d i f f e r e n t p a r t s of e a c h m o l d . H a v e you ever seen a whitish, p o w d e r y What is mildew?

material on shoes or leather j a c k e t s t h a t w e r e s t o r e d in a

a

your bread.

act like

roots by obtaining from the bread the

How are molds useful to man?

on

mold. Examine each one and make

ments are others that branch downward into the bread. These

growing

such

"athlete's

damp

place?

Or,

per-

haps, during a d a m p summer, you have seen the

s a m e k i n d of w h i t i s h

on curtains or fabric furniture ings.

Or,

you

may

have

spots cover-

seen

black

foot." S o m e m o l d s a r e useful, such as

streaks on sheets or pillow cases that

the ones which give

y o u r m o t h e r s t o r e d w h i l e t h e y w e r e still

flavor

to

certain

k i n d s of c h e e s e . B y f a r t h e m o s t

im-

damp.

B o t h the white spots a n d

the

p o r t a n t u s e of m o l d s is t o p r o v i d e t h e

black streaks were caused by

mildew,

basis for the d r u g s called

antibiotics.

w h i c h is t h e g e n e r a l n a m e f o r a g r o u p

These drugs have helped to

conquer

of p l a n t s v e r y m u c h l i k e t r u e

molds.

c e r t a i n d i s e a s e s t h a t t o o k t h o u s a n d s of

Mildews have a mycelium and sporan-

lives b e f o r e a n t i b i o t i c s w e r e d i s c o v e r e d .

gia. M i l d e w s not

S o m e antibiotics are penicillin, strepto-

leather a n d cloth, b u t they also destroy

mycin, and aureomycin.

m a n y useful plants, a m o n g t h e m roses,

only

stain

and

rot

35

SPORE CASE OF BREAD MOLD

Rotifers are tiny, multi-celled marine animals, and abound in fresh-water ponds that have become stagnant.

>

OOLINA

GLOBIGERINA

Radiolaria are marine protozoa noted for threadlike pseudopods. The related Foraminifera have pseudopods which protrude through holes in their shells.

lilacs a n d

willow,

plum,

cherry

p e a c h trees. T h e m i l d e w covers these plants with a mycelium through which it d r a w s n o u r i s h m e n t f r o m t h e p l a n t ' s cells.

This

destroys

these

RAGWEED A POLLEN A *Z

and

cells,

and

SPORES OF SCOURING RUSH Pollen are the tiny spores, or microspores, in seed plants. They are usually tiny specks of yellow dust.

t h e r e f o r e , kills t h e p l a n t . O b s e r v e m i l d e w p l a n t s in t h e

same

m a y have noticed that the yeast

h a d m a n y curious shapes. L e t us again

way that you observed molds.

observe yeast. A s before, mix a W h e n you were feeding protozoa, you made . L JJ. i yeast budding?

Jyeast

cells tiny

s p e c k of y e a s t i n a d r o p of w a t e r . P l a c e

of

a cover glass on the mixture. M a n i p u -

and water. A l -

l a t e t h e m i r r o r of y o u r m i c r o s c o p e s o

a mixture

t h o u g h y o u w e r e primarily interested in the p r o t o z o a ,

you

as to cut d o w n t h e light, a n d focus carefully o n t h e

yeast. 37

Y e a s t is a p l a n t . T h e r o u n d ,

or

A n o t h e r w a y i n w h i c h t h e b u d d i n g of

n e a r l y - r o u n d , cells t h a t y o u see a r e e a c h a separate yeast plant. T w o things that will p r o b a b l y c a t c h y o u r a t t e n t i o n imm e d i a t e l y a r e t h a t s o m e yeast cells seem

yeast How else does yeast budding differ from cell division?

t o h a v e l u m p s s t i c k i n g o u t of t h e m , a n d

cells

differs

f r o m m o s t cell divis i o n is i n t h e that

the

fact

new

cell

which grows

from

t h a t y e a s t cells a r e seen in c h a i n s . T h e s e

the b u d does not necessarily

t w o facts a r e closely related.

f r o m t h e p a r e n t cell. A l t h o u g h t h e p a r -

separate

e n t cell a n d t h e b u d d e d cell l i v e a s s e p a rate plants, they m a y remain

attached

t o e a c h o t h e r . A s b o t h t h e s e cells b u d in t u r n , a n d t h e b u d s g r o w t o full size, a chain

of f o u r

longer

chains

cells is f o r m e d . of y e a s t

Even

cells m a y

be

formed. However, the connection

be-

t w e e n t h e c e l l s is n o t v e r y s t r o n g , a n d , eventually, the chain breaks. If y o u s e a r c h a b o u t a m o n g t h e y e a s t c e l l s o n y o u r s l i d e , y o u m a y find c e l l s that have more than one bud. Yeast cells reproduce by a division called "budding."

When

t h i s k i n d of b u d d i n g t a k e s p l a c e ,

Y-

shaped chains m a y be formed. L i k e o t h e r cells, y e a s t p l a n t s r e p r o d u c e b y cell division. B u t i n s t e a d

of

dividing in t w o in the middle, a yeast cell g r o w s a b u d . T h i s b u d i s t h e l u m p

T h e r e a r e t h o u s a n d s of d i f f e r e n t k i n d s How are yeasts , , . _ useful to man?

t h a t y o u c a n s e e a t t a c h e d t o s o m e cells.

of yeasts. C e r t a i n , . , kinds are v e r y use;L ful t o m a n . T h e s e

J u s t a s i n o t h e r k i n d s of cell d i v i s i o n ,

a r e t h e o n e s u s e d i n t h e p r o c e s s of

t h e n u c l e u s s p l i t s i n t w o . O n e p a r t of

mentation.

the nucleus moves into the bud, and the

on sugar. A s they obtain their nourish-

other p a r t remains in the p a r e n t

cell.

m e n t f r o m s u g a r , t h e y c h a n g e it i n t o

T h e b u d is s m a l l a t first, b u t s o o n g r o w s

a l c o h o l a n d c a r b o n d i o x i d e g a s . T h i s is

t o b e t h e s a m e size a s t h e cell

from

t h e p r o c e s s c a l l e d fermentation.

w h i c h it b u d d e d . A s y o u w i l l r e m e m b e r ,

h o l is a v e r y u s e f u l c h e m i c a l .

t h i s is q u i t e d i f f e r e n t f r o m t h e t y p e of

When

M o s t yeasts live a n d

y e a s t is m i x e d

with

fer-

grow

Alcobaking

cell d i v i s i o n y o u h a v e o b s e r v e d . T h e r e ,

dough, the yeast plants grow on

t h e cell p i n c h e d i n t w o , f o r m i n g

two

s u g a r i n t h e d o u g h . T h a t is, t h e y e a s t

c e l l s e a c h h a l f t h e s i z e of t h e c e l l t h a t

ferments the sugar in the d o u g h to form

d i v i d e d . E a c h of t h e t w o n e w c e l l s t h e n

alcohol a n d carbon dioxide. This gas

g r e w t o t h e size of t h e cell f r o m w h i c h

forms b u b b l e s in t h e d o u g h , a n d

the

they came.

d o u g h swells. W h e n this h a p p e n s

we

38

the

say t h a t the d o u g h "rises." D o u g h t h a t

C a t c h a fly in y o u r h a n d . W h e n y o u

r i s e s b e c o m e s l i g h t a n d fluffy. W h e n t h e

s e e a fly r e s t i n g o n s o m e o b j e c t , s l o w l y

b r e a d is b a k e d , t h e h e a t d r i v e s off b o t h

m o v e y o u r c u p p e d h a n d close to

the carbon dioxide and the alcohol. All

insect. T h e n , with a sudden quick move-

t h e h o l e s a n d i n d e n t a t i o n s i n a slice of

m e n t , g r a b t h e fly. Y o u w i l l p r o b a b l y

b r e a d a r e t h e r e m a i n s of b u b b l e s of c a r -

h a v e to try this m o r e t h a n once. H o l d

bon dioxide.

t h e fly g e n t l y i n y o u r h a n d , a n d

then

p o p it i n t o t h e c o l l e c t i n g b o t t l e .

After

D i s s o l v e a t e a s p o o n f u l of s u g a r i n h a l f a How can you see , J „ fermentation?

tumbler of •» , , water. M a k e u p a r

fresh

t h e fly is d e a d , u s e y o u r t w e e z e r s

of

y e a s t a n d w a t e r . P l a c e a d r o p of

the

to

r e m o v e it f r o m t h e b o t t l e . P l a c e it o n a g l a s s s l i d e a n d m a n i p u l a t e it w i t h y o u r p r o b e so t h a t y o u c a n o b t a i n a

mixture

the

good

v i e w of o n e of i t s e y e s b e n e a t h t h e l o w p o w e r o b j e c t i v e of y o u r m i c r o s c o p e .

mixture on a cover glass a n d a d d a d r o p of s u g a r - w a t e r . M a k e a

hanging-drop

D o y o u s e e t h a t t h e w h o l e s u r f a c e of

p r e p a r a t i o n of t h e c o v e r g l a s s a n d i t s mixture. Leave the hanging-drop

t h e e y e is What does a fly's eye look like?

slide

in a w a r m place. A n h o u r later, p l a c e t h e slide u n d e r y o u r m i c r o s c o p e . y o u s e e t h e m a n y b u b b l e s of

Do

carbon

of

tiny

hexagonal

(six-sided) These

c a l l e d facets.

composed spaces?

spaces

are

E a c h o n e g i v e s t h e fly a

dioxide formed by the yeast's ferment-

s e p a r a t e i m p r e s s i o n of l i g h t a n d c o l o r .

ing action on the sugar?

In

other

words,

each

facet

acts

as

t h o u g h it w e r e a s e p a r a t e e y e . A n e y e m a d e u p of f a c e t s is c a l l e d a c o m p o u n d

Insects

eye. M a n y insects h a v e such eyes.

Obtain a small wide-mouth bottle with a lid. C o v e r t h e '.*

Where can you keep insects?

bottom

with

inside

blotting

paper, paper towels absorbent cotton.

or

Then

wet the material with household ammonia. ( D o not hold y o u r face close to the bottle when you are pouring ammonia, for it will c a u s e y o u r eyes a n d n o s e t o smart painfully.)

C a p the wide-mouth

bottle. N o w y o u h a v e a n insect collect o r ' s b o t t l e . If y o u p l a c e a n i n s e c t i n it, t h e a m m o n i a will q u i c k l y kill t h e specim e n w i t h o u t d a m a g i n g it a s might do.

swatting Insect eggs come in many different shapes and sizes.

39

, w

N o t e h o w the

fly's

eye bulges

out-

w a r d o n a l l s i d e s of t h e h e a d . I n f a c t t h e e y e s m a k e u p t h e l a r g e s t p a r t of t h e h e a d . B e c a u s e t h e eyes b u l g e o u t so far, t h e y e n a b l e t h e fly t o s e e i n a l l d i r e c t i o n s a t o n c e . T h i s is w h y it is s o h a r d

to

c a t c h a fly, f o r it c a n s e e a s w e l l b e h i n d a s i n f r o n t of i t s e l f . L o o k a t t h e fly's f o o t . N o t e t h e h a i r y How can a fly walk upside down?

pads

between

two

curving

claws.

Orion acrylic fiber, as seen under a microscope.

The

p a d s secrete a sticky s u b s t a n c e t h a t ena b l e t h e fly t o c l i n g t o s m o o t h s u r f a c e s . T h i s is w h y a fly c a n w a l k u p s i d e d o w n o n t h e c e i l i n g . L o o k a t t h e w i n g s of a fly. T h e " v e i n s " i n t h e w i n g a r e r e a l l y dried-up air tubes that connect with the fly's

breathing

organs.

T h e r e a r e m o r e k i n d s of i n s e c t s t h a n a n y o t h e r k i n d of a n i m a l . A s

insects

h a v e a n a l m o s t i n f i n i t e v a r i e t y of f o r m s and oddly-shaped organs, a

collection

of s e v e r a l d i f f e r e n t k i n d s w i l l p r o v i d e you

with enough

material

for

many

h o u r s of i n t e r e s t i n g m i c r o s c o p i c examiA filament of rayon yarn as seen under a microscope.

nation.

Fabrics You

may

already

H o w is cotton . . _ thread m a d e r

know

cotton

t h r e a d is m a d e f r o m ., .. , rp, the cotton plant. T h e fruit

p l a n t is a w h i t e

that

fluffy

of

the

cotton

material

much

l i k e a b s o r b e n t c o t t o n . T h i s is c l e a n e d and

spun into thread. B u t just

goes on in the spinning process? Nylon stocking weave as seen under microscope. 40

what You

c a n find t h i s o u t b y e x a m i n i n g a p i e c e

HOUSEFLY

, COMPOUND EYE