It would be a useless accomplishment for the cricket to be able to

sing, if there were no ears to hear its song. Nature has arranged that

his song shall not go unheard and if we examine a female cricket, that

is to say a cricket which has no sound-producing apparatus, we shall

find an oval depression, covered by a membrane, on each of her front

legs; these are her ears and they enable her to hear her mate calling

to her.

We have often heard the song of the grasshopper as we have walked

through the fields and he too will occupy our time for a few moments.

When he sings, he kicks his legs rather violently and this gives us a

clue to the situation of his vocal organs. The inside of each of his

hind thighs is ridged and the edge of each ridge is, as we can see

if we magnify it, rough like a file. This file-like ridge is rubbed

against a smooth ridge on the edge of the fore wing and the result is

the familiar note of the grasshopper.

This insect also has ears, but they are not easy to find unless they

are pointed out to us. If we examine a grasshopper we shall see that

its body is divided into three parts: a head, a solid portion from

which the wings and legs arise, the thorax and a portion (the abdomen)

made up of a number of rings or segments. On the sides of the first

of these rings, counting from the forward end, we shall find small

depressions covered with membrane, these are the ears. It is curious

that although many of the grasshoppers cannot give out a note, so far

as human ears can detect, they nearly all have ears; maybe there is a

grasshopper song which only grasshoppers can hear.

Very many other insects have sound organs, but they are nearly all

constructed on the same plan. It may seem surprising that sounds can be

produced by these simple means. Sound is really caused by waves in the

air and these insect vocal organs set up rapid sound waves, by their

vibration.

The microscopist should never be at a loss for objects derived from the

insect world: it is impossible to walk without treading upon some six

legged wayfarer. The wing cases of beetles are often of rare beauty,

some on account of their sculpturing, some because of a mantle of

scales.

In our greenhouse and garden we can find mealy bugs, curious little

powdered insects which do an enormous amount of damage. The fringe

wings, or Thrips, are common and destructive; examine their curious

feet and their beautifully fringed wings, the sight will repay you. And

lastly, if you number an insect enthusiast amongst your friends, enlist

his aid in gathering objects for your microscope.

CHAPTER XV

THE MICROSCOPE BY THE SEASIDE--ANIMAL LIFE

It is always surprising that the majority of microscopists never dream

of examining any of the hundreds of beautiful objects which can be

found by the seaside, in the course of an afternoon’s ramble. That

every pond will contain ample material for study, the microscopist

knows instinctively; insect life and plant life also he studies, but

the microscope is generally left at home when a visit is paid to the

seaside. A rocky coast is better than a sandy one, for rock pools yield

many objects, and the warmer southern waters of our coasts are better

than the colder northern seas, but the microscopist who finds himself

on a northern sandy coast need not despair, if he search diligently he

will find material enough to occupy him for many a day.

Nearly every rock pool will provide one or more Sea Anemones; it is

hardly necessary to describe these “flowers of the sea” as they have

been called, they are such familiar objects and the brilliant colouring

of some of them makes them highly attractive. In many respects Sea

Anemones resemble the _Hydra_, one of the pond dwellers, they are

rather more highly developed, however. Any Sea Anemone will serve our

purpose because we are about to examine the little darts with which its

tentacles, and even its body, are armed. If we find several different

kinds of Anemone, we must take the most transparent we can find and

also a small specimen; we can examine the larger, more opaque ones

later. Having transferred our specimen to a small jar, containing but

a small quantity of sea water, we wait till it has recovered from its

transfer and spread its tentacles, then it must be killed by one of the

methods suggested in our concluding chapter (see p. 306). One of the

tentacles must then be snipped off with scissors--some people cut off

the tentacle without killing the Anemone and the animal does not appear

to suffer a great amount of inconvenience, in fact a new tentacle soon

grows to take the place of the old one. We do not recommend promiscuous

vivisection. The tentacle is placed on a clean slide, a cover slip

placed over it and pressure is applied. An enormous number of little

thread-like darts are pressed from all parts of the tentacle. In some

cases, little oval capsules are squeezed out and, in the capsules,

the darts may be plainly seen, coiled up. On applying pressure to a

capsule, the contained dart will shoot forth, much as does a glove

finger turned inside out, when we blow violently into the glove. These

little darts are of the greatest interest to the microscopist; they

vary in shape according to the kind of Anemone, as we shall find if we

try this experiment with various Anemones. Some of them are straight

with stiff bristles at their bases; some have backwardly directed barbs

at their tips; others are apparently jointed, forming a zigzag, with

a short length of the dart going from left to right, the next short

length from right to left, and so on to the tip. It is marvellous how

the darts can be accommodated within the capsule, for the average

length of the latter is but 1/300 inch whereas its dart may measure 1/8

inch. These little threads contain a poison capable of paralyzing any

moderate-sized fishes which they touch.

Have you ever seen a “comb bearer” or as it is often called, a “marble

bleb?” Probably you have though you may not know its name. Sometimes it

occurs in rock pools, though more often it is found in one’s shrimping

net and occasionally it is washed up by the tide, but it does not live

long out of water. The “marble bleb,” as its name denotes, is an almost

globular mass of soft, transparent jelly. It is practically colourless,

with the exception of eight bright coloured bands which run from end to

end of the animal. To the naked eye, this little denizen of the sea is

of rare beauty: as an object for low-power microscopy it is entrancing.

When magnified, the bright bands are seen to be composed of rows of

flattened outgrowths. If our specimen is small enough to be examined

in water, its real beauty can only be seen in this manner, we shall

observe that the flattened outgrowths act like paddles, sometimes they

work all together, sometimes independently of one another and this fact

explains the marvellous evolutions of the “marble bleb” in water. Now

it shoots forward in a straight line with some rapidity, now it rolls

over and over and swims onward while doing so.

In the sun, it displays glorious iridescent colouring. At the hinder

end of the “bleb” we notice a pair of hollows: from these, as we watch

it swim, we shall see it suddenly shoot out a pair of long feathery

tendrils and they may be withdrawn into the hollows as suddenly. We

must make a point of examining the “marble bleb,” it is one of the gems

of our coasts.

Superficially the common, sponge-like “Dead man’s toes” or, to give it

its more pleasant title, “Mermaid’s fingers,” is a very drab affair. It

is a dirty-brown lobed, spongy mass with a leathery skin; when removed

from the water it loses all semblance of shape. In sea water, however,

if we examine it carefully, we shall see that it is studded with

beautiful little flower-like creatures, each one resembling a miniature

Sea Anemone. Examined, in water, under a low power of our microscope

we can see the water current flowing through the channels with which

it is perforated, after the manner of a sponge. If, now, we take a

dead specimen and cut it up, placing a small portion on a slide and

shredding it with a pair of needles, we shall find, when we magnify

the result of our work, that there are a number of minute mineral

spikes, called spicules, and very beautiful objects they make for the

microscope. There are many sea-side creatures, which we may find,

closely related to “Mermaid’s fingers,” they may all be treated in the

same way for they will all yield spicules which will repay us for our

trouble. All these spongy organisms are not provided with spicules as

ornaments, though one might be forgiven for thinking so, seeing how

decorative many of them are. Their presence is necessary to strengthen

the spongy material.

The specimen we have just examined is not one animal but a colony of

very minute animals. These colonies are very common, not only in salt

but also in fresh water. They serve a useful purpose, for the creatures

composing them are so minute that they would fare badly did they

dwell alone. Dwelling together as they do and each one contributing

its share to the building of the home they appear to thrive to a

wonderful degree. The coral islands are built, as to their foundations

at anyrate, by millions of very minute animals, living together in

colonies.

We mentioned the sponges a moment ago and many of them may be found

around our coasts; not the household sponges we know so well, but

much smaller, though equally interesting, colonies. Like the better

known sponges, those which we find on our shores are perforated with a

number of holes through which the water is driven by means of little

whip-like structures which line the cavities. Professor Grant has

graphically described his impressions at witnessing this water current

for the first time. “I put a small branch of the _Spongia Coalita_,” he

writes, “with some sea water in a watch glass, under the microscope,

and, on reflecting the light of a candle up through the fluid, I soon

perceived that there was some internal motion in the opaque particles

floating through the water. On moving the watch glass, so as to bring

one of the apertures on the side of the sponge fully into view, I

beheld, for the first time, the splendid spectacle of this living

fountain vomiting forth from a circular cavity an impetuous torrent

of liquid matter, and hurling along, in rapid succession, opaque

masses, which it strewed everywhere around. The beauty and novelty of

such a scene in the Animal Kingdom long arrested my attention; but

after twenty-five minutes of constant observation, I was obliged to

withdraw my eye from fatigue, without having seen the torrent for one

instant change its direction, or diminish, in the slightest degree, the

rapidity of its course. I continued to watch the same orifice, at short

intervals, for five hours, sometimes observing it for a quarter of an

hour at a time, but still the stream rolled on with a constant and even

velocity. About the end of this time, however, I observed the current

to become perceptibly languid ... and in one hour more the current had

entirely ceased.”

Frequently the sponge we examine may be found to be studded with many

yellowish spots; closer examination will show that these spots are

composed of very small jelly covered eggs. Later these eggs find their

way into the cavities of the sponge and are forced therefrom in the

currents of water. Each of the young sponges thus expelled is furnished

with a covering of little whips, by means of which it swims about till

it can find a suitable spot on which to anchor and complete its growth.

The Sea Anemone, which has already provided us with objects for our

microscope, has many near relatives which we must make a point of

examining, while we have the opportunity. Many of these creatures, or

rather their colonies, for they do not live singly, are to the naked

eye, strangely like seaweeds. A number of them are moss-like and may

be found on wooden breakwaters and similar situations when the tide is

low; they should be collected and examined and, to see them at their

best they should be examined under water. It is hardly necessary to

describe any one of these colonies in detail, for they are so numerous

that the one we described might not come into the hands of our readers

for a long time. In general characters they are all somewhat similar

so we will confine ourselves to generalities. For the most part, the

stems and branches of these colonies are of the thickness of thread. As

we watch them under the microscope we shall see that they are studded

with little cups and, presently, from each little cup there appears a

little tuft of tentacles which is waved about in the water. Each member

of the colony is similar to its neighbour and each one, again, is very

like the fresh water _Hydra_ with which we are familiar.

Of all the common objects of the sea shore one of the commonest

everywhere is the sea-mat. Nine people out of ten or, we might safely

say that everyone who had not learned its true nature, would guess it

to be a seaweed. As we find it washed up on the beach it is almost the

colour of sand, somewhat rough to the touch, whilst its whole surface

is pitted with minute holes. The sea-mat, when dry as we usually find

it, is a remnant of a colony of sea dwellers very similar to those

we have just described. From each little hole, in a living specimen,

which we can find without much difficulty, there appear the familiar

tentacles; each hole is the home of a minute hydra-like animal.

Hooke, whom we mentioned in our chapter on the History of the

Microscope, though a careful observer, was quite misled by the sea-mat;

he thought it was a seaweed, for he wrote: “I have not, among all

plants and vegetables I have yet observed, seen any one comparable to

this seaweed. It is a plant which grows upon the rocks under water

and increases and spreads itself into a great tuft, which is not only

handsomely branched into several leaves, but the whole surface is

covered over with a most curious knot of carved work, which consists of

a texture much resembling a honeycomb, for the whole surface on both

sides is covered over with a multitude of very small holes, being no

larger than so many holes made with a pin, and ranged in the neatest

and most delicate order imaginable, they being placed in the manner of

a quincunx, or very much like the rows of eyes of a fly, the rows or

orders being very regular which way soever they are observed. These

little holes, which to the eye look round, when magnified, appear very

regularly shaped holes, representing almost the shape of a round-toed

shoe, the hinder part of each being, as it were, turned in, or covered

by the toe of the next below it. These holes seemed walled about with

very thin and transparent substance, looking of a pale straw colour,

from the edge of which, against the middle of each hole, were sprouted

out four small, transparent, straw-coloured thorns, which seemed to

protect and cover those cavities.”

As a well-known author has remarked: “This is really a wonderfully

faithful description of the common sea-mat, and one cannot help

picturing the surprise and delight of old author Hooke, could he have

seen a portion of a living colony under a modern microscope.”

One of our finds may be the “Bird’s head.” It is a branched form,

quite unlike the sea-mat but it is of even greater interest. Under the

microscope, we shall see the many waving tentacles, but another feature

is sure to attract our attention, a feature which is responsible for

the popular name of the colony. On the outside of each cavity

containing a member of the colony there is a structure which resembles

nothing so much as a hawk-like bird’s head atop of a long neck. While

the tentacles wave in the water, the bird’s head snaps vigorously,

moved here and moved there. The birds’ heads, which might be mistaken

for parasites stealing food from the waving tentacles, really perform

the useful function of keeping them clean and warding off creatures

which might do them harm.

[Illustration:

_By the courtesy of Messrs. F. Davidson & Co._

1. A SECTION OF HUMAN SKIN

The corkscrew-like pores, leading from the sweat glands to the

surface, are plainly seen in the section.

2. THE FACE OF A FLY

A wonderful photograph, at 15 inches, taken by the micro-telescope.

Notice the very large size of the eyes relative to the rest of the

head.

]

Now let us pass to quite different though equally common sea shore

animals, the star fish. There are very many kinds but the common star

fish will serve our purpose well. We may make a beginning by examining

his back under a low magnification and observing that it is protected

by a number of hard plates which form a very efficient armour. At the

point where two of the rays (the finger like structures) arise we shall

notice a small flat plate, this too is worth a moment’s inspection, for

it is the water pore through which the star fish takes in water.

The under surface of the star fish shows us of course its mouth in

the centre of its body, the soft fleshy suckers which cover the rays,

with the exception of a narrow line down the centre of each one. At

the tip of each ray there is an eye; it may easily be distinguished by

its bright red colour and microscopic examination will show us that it

is quite unlike any of the other eyes we have examined. Over each eye

there is a little tentacle; these little tentacles may be called the

noses of the star fish, for, by means of them it is able to smell. They

are as unlike our idea of a nose as are the little pits on the feeler

of the cockchafer which we examined, yet these noses and ours all

perform the same duties. Our time will be well spent if we devote some

of it to a search for others less common star fish. Some of them are

really beautiful and whatever specimens we come across can be compared

with the common variety which is everywhere.

Closely related to the star fish are the sea-urchins. The relationship

may not be apparent at first sight but a careful study of an urchin

and a star will reveal many points of similarity. Our object in these

pages, however, is to find material for our microscope and not to

unfold the relationships of various members of the Animal Kingdom. When

we have learned to cut sections, we may try our hand at the spine of

a sea-urchin, it is an object well worthy of study. The hard shell of

the urchin may be examined under a low magnification, we shall see then

that his armour is far more highly developed than that of the star fish.

Another near relative of the two animals we have just described is

the sea slug or sea cucumber. Though an article of commerce of some

importance in the far East, the sea slug is not so common on our coasts

as its relations. We must make a point of finding a specimen, however,

for it provides us with one of the most remarkable objects for our

microscope that could possibly be imagined. One species, which goes by

the name of _Synapta Inhærens_, is the one most worthy of examination.

We must describe the creature first of all so that we may know what

to look for. It is aptly named sea cucumber for it is not unlike that

fruit--yes! fruit is correct, though the cucumber is more often called

a vegetable. The animal’s skin is tough and leathery and at the head

end there is a fringe of feathery tentacles. The sea cucumber must be

looked for amongst sea weeds or, maybe, he lies buried in the sand,

with only his fringe of tentacles on view. A friendly fisherman will

probably aid us in our search.

Having found our creature we must examine his leathery skin under the

microscope. To the touch it is evident that it is studded with some

flinty matter, but the microscope alone can show us the amazing beauty

of this armour. Under a low magnification, we can see, dotted over the

leathery skin, some nearly circular plates to each of which is attached

a little anchor. Now, from a dead animal of course, we must scrape away

some of these objects and examine them with a higher magnification.

Even the hardened microscopist will be delighted when he sees the

armour of the sea cucumber for the first time. Each anchor is hinged

to a little plate, each little plate, nearly circular in outline, is

perforated with seven holes, six round the circumference and one in the

centre and every perforation has a toothed margin. So perfect are these

minute plates and anchors, that the most intricate man-made machinery

could not have turned them out more perfectly to pattern. They are

precisely similar to one another in size and shape; as objects for the

microscope, even the sea with all its store of wonders, can offer us

nothing more marvellous.

We may number the sea mouse amongst our treasures of the sea-side.

Though called a mouse, on account of its curious movements and partly

perhaps because of its appearance, it is really a worm. It does not

appear to have the slightest resemblance to the common earth worm, nor

to the liver fluke which is described on another page, nevertheless,

it is related to both these creatures. The raiment of the sea mouse

is gorgeous in the extreme; on its back is soft brownish hair, its

sides are clothed with yellow and green hair, displaying a wonderful

iridescence and amongst the hair on the sides there are many stiff

brown bristles. Of the covering of the sea mouse it has been said:

“It is as if all the hues of the rainbow were collected there, making

this remarkable animal a living jewel, and truly worthy of the name of

Aphrodite, the Queen of Beauty.” The bristles of this creature we must

examine microscopically, they vary in structure according to the kind

of sea mouse, for there are several kinds, but in some of them they are

formidably barbed, in all of them they act as a protection.

Many other worms, a number of them un-wormlike in appearance will claim

our attention but we cannot devote more space to them here. There is

the common shell-binder, a curious worm, which builds for itself a

still more curious shelter of broken shells. Another worm, _Serpula_

by name, also lives in tube-like structures of its own manufacture and

is remarkable in that a row of nearly two thousand seven-toothed hooks

run along its back and all these thirteen thousand odd teeth are there

merely for the purpose of holding _Serpula_ in its tubular home.

Much interesting work may be done at the seaside in studying the young

stages of various familiar creatures. This work, however, necessitates

the keeping of the adults in an aquarium; for the young ones, in most

cases, are so unlike their parents that, if found swimming about on

their own account, they would never be recognised. Young barnacles,

for instance, have six legs, a tubular mouth and a single eye. At a

later stage they might be mistaken for young shell fish; they possess

a shell, not unlike that of the mussel, containing, however, not a

soft, fleshy mollusc but a six legged creature which swims through the

water in jerks, after the manner of a water flea. Strangely enough, it

is now provided with two stalked eyes like those of a crab, whilst of

mouth parts it has none, or they are so imperfectly developed as to

be useless for feeding. Soon this active youngster settles down for

the rest of its life and becomes a sedate and sedentary barnacle, with

one imperfectly developed eye and a mouth capable of feeding to good

purpose.

Young crabs are equally curious and also totally unlike their parents,

but these curious creatures are hardly accessible to those who only pay

a flying visit to the sea-side. As we have remarked, an aquarium is a

necessity and to keep marine animals inland is a feat beyond the powers

of the ordinary mortal.

The Sea Lemon or Doris is a curious little creature, worthy of

examination. Its habit is to feed upon sponges and strange diet it

is, for we remember that all sponges are fortified with hard flinty

structures, called spicules. This habit of the Sea Lemon is of use to

the microscopist, for the stomach of the creature is always laden with

the indigestible spicules and a very interesting collection of these

beautiful structures may be gathered together in this manner. The egg

masses of Doris may be looked for on rocks during the summer. Enormous

numbers of eggs are laid in a jelly-like mass. Some of this jelly may

be collected and examined under the microscope and, should we have

collected our material at a favourable moment, we may watch the eggs

hatch and observe the young Sea Lemons in their delicate transparent

shells swimming round and round the chamber within which they are

imprisoned during the very early stages of their lives.

Very frequently in the summer, when the seas are warm any agitation

of the water causes a beautiful phosphorescence to appear.

Phosphorescence, by the way, may be described as light without

heat and it is not uncommon in nature. Glow worms and fireflies are

phosphorescent; fish, also, in the dead state, often emit a certain

amount of light as do bones whilst, of course, phosphorous itself is

the best example of a naturally phosphorescent body. Phosphorescent

sea water, however, owes its peculiarity to myriads of minute animals

and they will afford us an interesting half hour with the microscope.

Let us collect a little of this water in a glass jar and take it into

a darkened room that we may the better see the phosphorescence. When

the water in the jar is undisturbed, we can see nothing unusual; if

we stir it or strike it a faint greenish light is given off, but it

does not last for long. Now, on taking the jar into the daylight, as

soon as our eyes are accustomed to the light, we shall just be able

to see that there are some very small living creatures on the surface

of the water. We must examine one, under a fairly high magnification;

it may be transferred, from the jar to a drop of water on our slide,

by means of a paint brush. The little animal which is responsible for

the phosphorescence of sea water is strangely reminiscent of an apple

with its stalk. It is, of course, very minute being only 1/60 inch

in diameter and its tail, which we have compared to the stalk of the

apple, is equal to the diameter in length. The whole creature is quite

transparent. As we watch it swim in our drop of water, we shall notice

that it propels itself by the lashing of its tail.

There are countless animals of the sea we have not so much as

mentioned, but the marine gardens contain plants so interesting and so

totally unlike those which live upon land that we must devote a few

pages to them also.

CHAPTER XVI

THE MICROSCOPE BY THE SEASIDE--PLANT LIFE

The plant life of the sea side may be divided into two natural groups

(i) of plants living on the shore near the sea and (ii) of plants

living in the sea, for part of each day at least. The former group

contains many plants of exactly the same kind as occur far inland,

together with a few typically sea-side plants such as Thrift or Sea

Pink. They are, however, one and all land plants. In this chapter we

shall confine ourselves to the real sea plants, the seaweeds.

Before we study any of these interesting plants under the microscope,

it will be useful to learn a little about seaweeds in general, because

they are so totally unlike land plants in every respect. They belong to

the great plant division known as the _Algæ_, to which also belong the

Diatoms, Desmids, _Volvox_, _Spirogyra_ and many of the other plants

we mentioned in our chapter on Pond Life. So we see that, although all

seaweeds are _Algæ_, not all _Algæ_ are seaweeds. They are higher in

the scale of development than Fungi, to which Bacteria, Yeast, Mould,

etc., belong, though they are not so highly developed as Ferns and not

nearly so advanced as flowering plants. A very short acquaintance with

_Algæ_ will show us that they are either green, brown or red. The green

_Algæ_ are nearly all fresh water forms, though a few are to be found

in the sea; on the other hand brown and red _Algæ_ are common in the

sea and rare in fresh water.

As we study our seaweeds on the shore, if we are really observant,

we shall notice that they live in zones or belts according to their

colour. There are exceptions to this rule but, in general, the green

seaweeds dwell in situations where they are only covered by the sea

at high tide; the red seaweeds are to be found mostly where they are

always below water and, between the two, the brown seaweeds occur.

In some parts, this colour scheme is very striking. Frequently red

seaweeds may be found above high-water mark it is true, but in such

cases they nearly always occur in rock pools and they are invariably

sheltered by brown seaweeds.

In our chapter on plant life we mentioned that many coloured plants

contained the green colouring matter, chlorophyll, just as do the

ordinary green leaves. We showed too that by boiling some green leaves

in methylated spirits we could extract the chlorophyll and that its

solution had the peculiar property of appearing green when light passes

through it and red when light is reflected from it. If now we take

almost any brown or red seaweed, we cannot see a trace of chlorophyll

anywhere. Let us leave our specimen, however, in fresh water for a

few days when we shall find that the brown or red colouring matter as

the case may be, is dissolved by the water and a green plant remains.

By treating the seaweed, deprived of its distinctive colour, with

methylated spirit as described above, we can obtain a solution of

chlorophyll.

The microscopist who is anxious to make a study of seaweeds, will

find little scope for his hobby on a sandy shore. Just as the most

interesting marine animals are to be found where rocks abound, so must

we hunt in similar situations for our _Algæ_. A few thread like _Algæ_

are able to anchor themselves to the sand but most of them require

a substantial support. A bare rock is a much favoured situation and

before we have learned the peculiarities of these plants we may marvel

how they obtain any sustenance from so barren a resting place. As a

matter of fact they derive no nourishment from the rocks on which they

rest. The part of the sea weed which, in our ignorance, we may have

dubbed a root, is nothing of the kind. It bears no relationship to the

roots of higher plants and is a mere anchor, designed to fasten its

owner to a support.

None of these plants have roots, none have true stems or leaves, though

the parts resembling stems and leaves are often so called; none of them

flower and so fruits and seeds are unknown to them. Their food is

absorbed from the sea water over the whole of their surface.

We may well begin our study of the seaweeds with an examination of the

external structure of as many different kinds as we can find. Some of

them are flattened and very thin forms and of them the Sea Lettuce may

be taken as typical. This plant, known to scientists as _Ulva Lactuca_,

occurs at high-water mark. In its fully developed form it is pale

green and so thin as to be almost transparent; its structure may be

studied under the microscope without difficulty. Then there is the very

common, green, Compressed Enteromorpha which grows in great profusion

on the rocks of the shore, rendering them exceedingly slippery. The

closely related Intestinal Enteromorpha as it floats in the water

resembles a green, membranous tube and those of us who have ever done

any zoological dissection will appreciate how well named this plant is.

The structure of both the Enteromorphas can easily be seen. Many of the

brown and red _Algæ_ will provide us with a good deal of occupation

in making out their structure. Some of them, the brown _Ectocarpus

Siliculosus_ for example, may be found, growing in moss like tufts,

which are usually attached to one of the larger _Algæ_ living between

the tide marks. It is one of the simplest of the brown sea weeds,

consisting of branched threads, but one cell in thickness. The Wracks,

of which the Common Bladder Wrack or Pop weed with its little air

filled bladders is familiar to everyone, are more complicated in

structure, in fact they appear to be possessed of stems and leaves, but

we shall return to them in a moment.

Most of the common red _Algæ_ are so delicate in structure that they

require a fairly high magnification for their examination. The thin,

membranous fronds of the beautiful crimson _Delessera Sanguinea_, may

be sought below low tide limit or may be found washed up upon the

shore. Superficially the plant resembles a red hart’s-tongue fern, with

much more delicate fronds than ever fern of that species possessed. We

may well compare its structure with that of the sea lettuce, for it is

equally transparent.

In the rock pools of many parts of the coast we may happen upon a

most curious almost white sea weed, known as Coralline or _Corallina

Officinalis_. Its branched, feathery stems are hard and stony and the

whole plant bears a superficial resemblance to a coral, hence its name.

The plant absorbs a substance known as calcium carbonate from the sea

water and deposits it in the form of a hard, stony covering over its

surface. Calcium carbonate does not occur in sea water everywhere, at

least not in sufficient quantity to be of use to the Coralline, that is

the reason the sea weed is not quite so common as some of the others we

have mentioned. The curious armour-plating of this sea dweller, should

be studied under the microscope.

The chief scientific interest of the sea weeds, however, lies in

their mode of increase, it is so totally different from that of any

of the higher plants. The most simple method of increase is known as

vegetative reproduction, it does not occur in every kind of seaweed

and is nothing more or less than the growth of a broken piece of plant

into a new individual. This form of increase is not unknown higher in

the plant world; begonia leaves may be induced to send forth roots and

grow into new plants, many garden favourites are propagated by means

of cuttings and both these methods are similar to the breaking away

and growth of portions of a seaweed; the garden plants, however, are

assisted by man, the seaweed does its own work.

The simplest forms of increase occur amongst those giants of the

sea, the Laminarias or Tangles as they are often called. These brown

seaweeds often attain enormous sizes, they all grow below the limits of

low tide and appear to thrive best where the water is frequently lashed

by storms. To see these plants at their best we must look down upon

them in their watery home. There are spots on the North-Eastern coast

of Ireland, where one may look from the cliffs upon a veritable forest

of Tangles. There thrives the “Devil’s Apron,” short of stem but with

a flat ribbon of a frond, which may attain a length of a dozen feet

and a width of as many inches. There too we can behold the Fingered

Tangle, with stem, maybe, six feet in length and a crown of large

finger-like fronds, “Sea Laces” or “Dead Men’s Ropes,” with fronds

resembling slender ropes, in length, at times as much as forty feet,

ride gracefully on the ever changing currents. Safely hidden in this

marine forest lurk queer fishes and crabs and shell fish. About the

broad fronds of the “Devil’s Apron” sea mice and sea cucumbers disport

themselves; the Tangle home is a paradise for marine life. Yet with all

their vigorous growth they increase simply by liberating spores which

give rise to new plants.

In our chapter on Plant Life we described spores very briefly; we said

that from a strictly scientific point of view they were not comparable

to seeds but that for our purpose they might be looked upon as seeds

for the reason that, by their germination, new plants were formed.

All the spores of land plants are minute, they are carried from the

mother plant to suitable spots for germination by wind. The spores of

seaweeds also are small, but they are very different to the little

wind-blown, land-dwelling spores. They possess a pair of the curious

little whip-like structures we have observed in so many water plants

and animals. By the lashing of these little whips they are able to swim

about in the water till they find a suitable spot to settle down and

grow into plants similar to those whence they came. On account of their

animal-like movements they are called zoospores.

The formation of zoospores may be easily observed in the brown sea weed

_Ectocarpus Siliculosus_ we have already mentioned. This plant, as we

have already remarked, consists of thin, thread-like rows of single

cells and from time to time it is branched. At certain periods of the

year, moderately large, pear shaped swellings occur on the threads of

the sea-weed. If we are either fortunate or exceptionally patient we

may chance to be examining one of these swellings under the microscope

at the moment when it bursts and sets free its contents. Should we have

this good fortune we must hasten to magnify more highly the zoospores

which have escaped from the pear shaped spore case. Here we may add the

caution that we shall only witness the bursting of the spore case if

we examine our specimen in sea water; we should require more than the

patience of Job to watch for its bursting in the dry state, for it will

never come to pass.

A careful study of a zoospore will show that it swims in a peculiar

manner. One of the little whips is directed forwards, the other

trails behind. After a short period of activity the zoospore comes to

rest, loses all means of propulsion, germinates and grows into a new

_Ectocarpus_ plant.

Sometimes this _Algæ_ reaches a low ebb of vitality, it requires a

new lease of life as it were, when this state is reached another

form of increase takes place. The events in this case may also be

witnessed under the microscope. From very similar spore cases a number

of zoospores are liberated and for a time they swim about freely. If

now we watch carefully we shall notice that one of the active little

bodies comes to rest and that the others lose no time in swarming round

it. One of these swarming zoospores fuses with the individual which

first ceased swimming about, with the result that a much larger,

non-swimming individual is formed which, after a short resting period,

germinates and grows into a new sea weed. The remainder of the

zoospores will come to rest later and germinate to form new plants just

as though no fusion had taken place with two of their number. Here we

see the beginnings of male and female increase amongst sea weeds; the

individual which first comes to rest is looked upon as the female and

the one with which it fuses as the male.

[Illustration:

_By the courtesy of Messrs. F. Davidson & Co._

THE FEELER OF A COCKCHAFER

The end of the feeler consists of a number of plates, which can be

spread fanwise. The pores visible on the plates are the insect’s

organs of smell.

]

Amongst the Wracks, of which there are a number of kinds, the methods

of increase reach a higher stage. First of all let us describe the

plants, so that we may know what to look for. They all belong to the

group of brown _Algæ_. The “Channelled Wrack” is, when fully grown,

about six inches long. It is much branched, often almost yellowish in

colour and grows just below high-water mark. Along one side of the

plant there is a moderately deep groove. Here we may note that the

Wracks grow in zones from just below high water mark to low water mark.

A little nearer the sea than the haunts of the Channelled Wrack, we

shall find the Flat and Bladder Wracks. The former is but six inches

or so in length, with flat, forked fronds, along the centres of which

runs a single rib. The Bladder Wrack varies considerably in size. It

may be smaller than either of the Wracks we have already mentioned or

it may be two or three feet in length. It is the one seaweed familiar

to everybody. Nearer to low tide mark we shall encounter the Knobbed

Wrack, greenish brown in colour and often as much as six feet in

length. It is so named because from the sides of its flat, leathery,

strap-like fronds, there arise little stalked bladders. Right at,

and often beyond, low tide mark there dwells the Notched Wrack; very

similar to, though larger than, the Flat Wrack, from which it may

easily be distinguished by the fact that the edges of its fronds are

toothed, after the manner of a saw.

It is obvious that the structure of any one of these Wracks is much

more complicated than is the case with _Ectocarpus_. The latter Alga

was composed of a number of cells, similar to one another in every

respect except size. If we tease a stem or a frond of one of the Wracks

upon a slide and examine the result of our efforts under the microscope

we shall see that the cells which compose the Wrack are not by any

means similar to one another. Those of us who have mastered the, by

no means difficult, art of section cutting, should cut sections of

stem and frond and compare them with sections of leaf and stem of some

higher plant. The comparison will show us that, although the seaweed

does not exhibit the complicated structure of a flowering plant, it

has at least three kinds of different cells--an outer layer, a central

structure and an intermediate layer.

If we secure a specimen of the Channelled Wrack, at the end of the

summer, we shall notice that the tips of certain of the fronds are

swollen. Examination of these swellings under a low magnification will

reveal a number of wart-like structures, and at the end of each wart

there is a little pore. If we open up one of these little warts, very

carefully with our mounted needles, we shall find that each little pore

opens into a cavity, within which we can find two kinds of structures,

hidden amongst a number of hair like growths. We shall see a number of

dark, oval bodies, at the base of the hairs, these are the egg cells;

more careful search will show us a number of much branched structures

also partly concealed by the hairs, these are the male organs of the

plants. The purpose of the hairs, by the way, is to keep the little

chamber moist, when the plant is left high and dry. If we watch the

pores of the other warts carefully we may be fortunate enough to see

the process of increase taking place, for it occurs outside the plant

and not within the chamber. The egg cell divides into two and its

contents pass out of the chamber by way of the pore; each cell of the

male organs gives rise to sixty-four oval little structures, each

provided with a pair of minute whip-like threads by means of which

it swims from the chamber and goes in search of the egg cells. Many

of these little navigators are lost by the way but one of them will

reach and fuse with each egg cell. After fusion the new-formed cell

germinates at once into a new Channelled Wrack.

That this is an advance is shown by the fact that the little swimming

bodies which fail to fuse with the egg cell, do not develop into new

plants as in _Ectocarpus_ nor does the egg cell, which has failed to

fuse with a swimming body, germinate.

In the Bladder Wrack, a very similar process takes place. There are,

however, certain important differences, differences which show that the

plant is still more highly developed. If we examine the cavities, in

the little warts of the Bladder Wrack we shall find that some of them

contain egg cells, some contain male organs but none contain both. We

noticed that the egg cell of the Channelled Wrack produced two eggs,

that of the Bladder Wrack produces eight. In other respects the two

plants behave similarly.

The methods of increase amongst the red seaweeds are rather more

complicated and as our object is to interest and not to puzzle

our readers we will content ourselves with a few general remarks.

Microscopists who are anxious to probe more deeply into the subject

will soon devise ways and means for themselves. The little swimming

bodies which lend an added attraction to the study of the brown

seaweeds are replaced, amongst the red _Algæ_, by organisms with but

one whip-like structure apiece and that without the power of propelling

its owner through the water. As with _Ectocarpus_, increase may take

place in two ways. On these red plants we may find the now familiar

swellings, which we have learned to know are spore cases, but instead

of the multitudes of free swimming organisms which are set free on

the bursting of the brown sea weed spore case, we now witness the

expulsion of but four inert spores, which settle down in the water and

immediately grow into new plants.

In the second method of increase, where male and female organs are

concerned, we find that both these structures grow on the outside

of the plant and not in cavities. Let us take the common, pink,

much branched seaweed, known by the fearsome name of _Callithamnion

Corymbosum_ as our example. The male organs grow in little fungus

like tufts about the branches of the plant and they give off enormous

numbers of little organisms which have no power of swimming to the

female organs. Either on the same or on another plant we shall find

the female organs; we need not describe them in detail but there is

one point of very great interest. From each of the female organs there

grows a long jelly-like hair. As we have remarked, the organisms set

free by the male organs cannot swim about but float aimlessly in the

water. Obviously the majority of them simply perish, one perchance may

touch a sticky hair to which it adheres, with which it fuses and passes

down to the female cell, resulting in the production of a new seaweed.

It may be remembered that in writing about the pollen grains of

flowering plants, we mentioned that those plants dependent upon

wind for the distribution of their pollen, have stigmas ingeniously

contrived for catching and retaining the grains. It is curious that the

red seaweeds should have very similar contrivances for capturing and

retaining the male cells.

The sea will also provide us with a rich harvest of those beautiful

microscopic objects, the Diatoms. They may be sought on seaweeds, their

yellowish brown colour often betrays their whereabouts, on rocks and

sand and in mud. The salt water forms are as varied and as beautiful as

their fresh water cousins.

To the microscopist who merely uses his microscope for the pleasure he

can derive from it, rather than for serious study, it may appear that

the plant life of the sea falls short of the animal life as far as

interest is concerned. He may disabuse himself at once of this idea.

There is no class of plants more interesting than the seaweeds and in

few branches of plant life is there greater scope for new discoveries.

The garden of the sea is largely an unexplored territory and there

is no coast-line in the world of equal extent which provides so many

different sea dwelling plants as our own.

CHAPTER XVII

THE MICRO-TELESCOPE AND SUPER MICROSCOPE

Those of our readers who have borne with us thus far may quite

excusably have thought that the last word had been attained in the

construction of the microscope. It is true that different makers

have made various improvements to their instruments, from time to

time in recent years, most of them of minor importance but useful

in the aggregate. But a few years ago, however, the advent of

the Micro-Telescope and Super-Microscope marked an epoch in the

manufacture of the microscope. We have shown that great strides

were made in scientific investigation when the first simple lenses

were manufactured, that there was a lull in microscopic research

till the appearance of the compound microscope and now, when the

latest instruments are in the hands of scientific workers, further

possibilities are opened up.

In all microscopes--the best as well as the cheaper instruments--there

is one failing which very early forces itself upon the user. They

have very little “depth of focus.” Let us explain exactly what the

phrase means. Once or twice in our pages, we have recommended that the

fine adjustment should be rotated to and fro while certain objects

are being examined. When potato starch grains, for instance, are

magnified sufficiently highly to show their characteristic markings,

the whole of the grain cannot be seen clearly at one time, because

at that magnification the “depth of focus” is slight. The higher the

magnification the less is the “depth of focus”; when this quality is

absent altogether only one plane of an object can be viewed clearly

without re-adjusting the focus. With low magnifications, we may, to a

limited extent, have more than one plane of an object in focus.

The same question of “depth of focus” occurs in photography and perhaps

an example showing how it affects the camera user may make the matter

clearer. Suppose we wish to photograph a landscape having, let us say,

a tree in the foreground, a cottage in the mid-distance and a hill in

the distance. If our lens is one of large aperture, that is to say

admits a considerable amount of light and is also what is known as a

long focus lens we shall find, when we view the scene on the ground

glass, that when the tree is sharply focussed, the cottage and hill

are not clear. When we rack in the camera to get the cottage sharply

focussed, the tree and hill will be un-sharp. Similarly when we focus

on the hill the tree and cottage remain out of focus. The reason is

that the lens in our case possesses little “depth of focus.” The

experienced landscape photographer, did he wish all three objects to

appear equally sharp could easily attain his object. He would perform

the simple operation known as stopping down his lens, that is to say

he would gradually close its diaphragm, while viewing the scene on

the ground glass. At a certain point everything would be sharp, from

foreground to distance. At the smaller aperture of the lens, caused

by closing the diaphragm, the depth of focus would be considerably

increased, at the same time much less light would be admitted to the

camera. Looking upon our object, under the microscope, as comparable

to a landscape, seen on the ground glass focussing screen of a camera,

it is obvious that, unless our object has no thickness, and this is

impossible, we cannot highly magnify its upper and lower surfaces

at one and the same time. There are no adjustable diaphragms in the

objective so our only course is to examine the two surfaces in turn or

to resort to a lower magnification.

[Illustration:

_By the courtesy of Messrs. F. Davidson & Co._

THE MICRO-TELESCOPE

1. View taken with ordinary camera. The arrow shows the building

illustrated in the plate below; it is 3/4 mile away.

2. The building indicated by the arrow in the plate above, taken from

the same standpoint through the micro-telescope.

]

Apart from any other consideration, the super microscope marks a big

advance from the fact that it possesses great “depth of focus.” It is

possible, for example, with this remarkable instrument to examine a

moss as it grows, with a high magnification and see not a portion of

a leaf or a fragment of the stalk, as with the ordinary microscope,

but the whole upstanding plant, in stereoscopic relief. It shows us

objects exactly as we should see them were we endowed with super eyes,

enormously enlarged, in relief and erect. Objects viewed through this

instrument are not inverted, as with the ordinary microscope.

[Illustration]

A is the microscope proper and is, in all respects, similar to the

instrument with which we are familiar, except that its mirror and

condenser have been removed. In the fitting provided for the condenser

a second microscope is arranged.

[Illustration]

This consists of a tube D, an objective F, an ocular C and an inner

sliding tube E, the whole fits into the metal case B, G is a stage on

which the object is placed and below G, if necessary, a condenser may

be fitted.

The instrument owes its remarkable magnifying powers to the fact that

the additional microscope B, forms a magnified image of the object on

the stage G, at the opening in the stage of the microscope A. This

magnified image is still further enlarged by the original microscope.

In other words, the power of one microscope is employed on that of

another.

The apparatus as we have described it gives enormous magnifications

and it is possible, by using a suitable combination of objectives,

to obtain a magnification of ten thousand diameters. Expressed in

non-technical language, a circle whose actual diameter is equal to

the thickness of the paper upon which these words are printed, could

be so magnified by the super-microscope that it would appear to be as

thick as ten thousand similar pieces of paper but, with this enormous

magnification, it is obvious that, even with such a marvellous

instrument, the whole of the circle from edge to edge could not be

seen at one time. With an ordinary microscope a magnification of one

thousand three hundred diameters is considered highly satisfactory.

So that there is a great probability of being able to see some of

the minute objects which are known to exist, but which have, up to

the present, eluded those who would view them, on account of their

minuteness. There is a possibility also of discovering a new underworld

of which no man has yet dreamed. The man who uses his microscope solely

because of the pleasure he derives from it, rather than he who uses it

because it is essential to his business or profession, will be more

attracted by the micro-telescope. By this we do not infer that the

instrument is not useful, as a fact it is of the greatest importance in

certain cases, especially for Nature-study work, for the observation

of minerals and to the chemist.

Like its sister instrument, the micro-telescope consists of an ordinary

microscope to which is attached a specially designed object glass in

a tube, which take the place of the condenser. The makers, indeed,

provide two of these object glasses--one for viewing objects from one

to two feet away, the other for viewing objects from a distance of

three feet to the planets, if need be. Once when the instrument was

being tested some crumbs were placed on the floor at a distance of

four yards and strongly illuminated, and the microscope with a 1-inch

objective focussed on the crumbs. With this objective in an ordinary

microscope the magnification would be about thirty diameters. Presently

some mice came out, and made themselves at home with the crumbs. The

mice could be examined at this distance, without their being aware of

it, so well that individual hairs were easily visible and about half a

mouse was in the field of view. In point of size each mouse appeared

about the same as a beaver within a foot or two.

Messrs F. Davidson & Co., 29 Great Portland Street, London, are well

known for the high state of perfection to which they have brought the

micro-telescope and other instruments connected with microscopy.

The novelty of the micro-telescope will appeal strongly to the Nature

lover. At a distance of a few feet a spider can be magnified to the

size of a large cat, and it can be watched spinning its web with

spinnerettes the size of teacups. Ants at a distance of six feet are

seen to be fearsome individuals, six inches in length, and their

tiny burdens are so magnified that they appear like yule logs or

goodly-proportioned boulders, according to their nature. At a distance

of ten feet a wasp may be seen scraping tiny shavings of wood from oak

palings by means of its jaws--shavings which it converts into paper

for building its nest. Very small insects may be observed as they come

into the world from their chrysalis stage. The never-tiring jaws of

the caterpillar may be seen at work devouring some favourite leaf--the

whole action of biting and swallowing the vegetable matter can be

plainly seen. Such interesting events as the tending of green flies by

ants, the leaf-cutting habits of the leaf-cutter bee, and a hundred and

one other events are all revealed by the micro-telescope and at such a

distance that the living objects are not disturbed in their activities,

being quite unaware that they are under observation. To the botanist

the instrument is no less useful.

In various manufactures, such as ore smelting, and in the manufacture

of glass, china and pottery, in enamelling and in certain engineering

shops, where it is necessary to examine material at a high temperature,

the micro-telescope is a great boon, and, at least, is the means

of avoiding considerable physical discomfort. It is used also by

architects and surveyors for examining the condition of the factory

chimneys, bridges, derricks and the like. To the engineer the

instrument is invaluable; we have explained elsewhere how necessary it

is that various metals and mixtures of metals should be examined for

fractures. Under the high magnification with the ordinary microscope,

even with an instrument specially designed for the work, only a

very small area can be studied at once. With the micro-telescope a

relatively large area may be examined under a high magnifying power.

There are three features of this ingenious apparatus which cannot fail

to commend themselves equally to the casual worker and the serious

microscopist. All objects are seen erect, just as the eye sees them.

This is brought about because, as in the case of the super-microscope,

we really observe a magnified, inverted image of our object, formed at

the spot where the object would be placed were we using an ordinary

microscope. This image is inverted once more in the microscope and so

it appears to us erect.

All objects appear in relief and in their proper planes; this is seen

in a striking manner by viewing an ordinary photograph through the

apparatus, when the various parts stand out as in nature. There is also

enormous depth of focus. With the attachment for viewing objects at a

short distance, the whole of a tubular shaped flower such as a daffodil

may be in focus at once, from the tip of the petals to the bottom of

the tube. With the attachment designed for long distance work, objects

from twenty yards to sixty miles may be clearly viewed at one and the

same time.

A few of the unsolved problems confronting the microscopist are

reviewed in our concluding chapter. Whether they will ever be solved

we dare not venture to say; but, if they are to be, surely to this

latest arrival in the microscopic world and to its companion, the

super-microscope, the honours will go.

CHAPTER XVIII

CHEMISTRY AND THE MICROSCOPE

To thoroughly comprehend the various uses to which the chemist may put

his microscope, it is necessary to have a knowledge of chemistry. The

science is so wide in its scope that no single chapter could do justice

to it. There are analytical chemists, scientists whose aim is to find

out the composition of various substances; biological chemists who deal

with the many problems of life in which chemistry plays a part, but we

need not attempt to detail all the branches of this highly specialised

science.

Chemical analysis is founded upon the fact that when certain

chemicals are mixed together they will, or they may, unite to form

quite a different chemical. This newly formed chemical is probably

a different colour to the substances which were used in its making,

or again the original chemicals may be soluble in water and the new

chemical insoluble, in which case it will form a cloudiness known as

a precipitate. An example may help to make our description clearer.

Suppose we take some common table salt and dissolve it in a little

water in a glass, then add to this a little solution of nitrate of

silver, which is sold under the name of lunar caustic, we shall find

that a white cloudiness is formed when the liquids mix, although

originally they were both clear. The reason of this cloudiness is that

the two substances, dissolved in water have united with one another to

form a third substance which will not dissolve, therefore it settles

down as a fine powder. Long experience has taught analytical chemists

exactly what chemicals to add to test for all the common substances, by

the formation of these precipitates; so that, if any powder were given

to one of these scientists he could tell its composition by applying

certain tests. In this chemical analysis considerable quantities are

required and it is often necessary to test very small samples, so small

that the ordinary methods are out of the question. This is where the

microscope scores, because with this wonderful instrument, only drops

are required and tests of corresponding delicacy may be made; in fact,

by modern microscopic methods it is possible to detect the presence of

as little as ten thousandth part of a grain of arsenic, or quicksilver

or of the deadly poisons, Strychnine or Prussic Acid.

In testing for poisons the microscope is invaluable. Frequently only

the most minute traces of the poison occur in the system and the modern

microscopist who makes a study of poisons and their detection can

solve mysteries which would have baffled all the scientists in the

world in days gone by.

Our chemical studies with the microscope may well begin with various

common crystals; they are usually easy to prepare; the process of

crystallization is always interesting to watch, and as objects for the

microscope it would be difficult to find anything more beautiful than

these home-made gems. All crystals should be examined by reflected

as well as by transmitted light. When we are working with the former

lighting, a piece of black paper beneath the slide will help to show up

the objects to better advantage.

The easiest method of obtaining crystals of any substance which is

soluble in water is to make a saturated solution in this liquid, to

put a small drop upon a slide, then to tilt the microscope slightly so

that there is a thin film of solution at the upper side of the drop.

The microscope must not be tilted so much that the liquid runs from the

slide on to the stage. Where the film of liquid is thin crystals will

be found first. A word of explanation is necessary concerning the term

saturated solution, especially as we may have occasion to use it many

times. When we add a solid to a liquid in which it is soluble, we shall

find that the liquid will take up a certain amount of the solid and no

more; when, on the addition of more solid it fails to dissolve, we have

reached the saturation point. A saturated solution then is a liquid in

which the maximum amount of solid is dissolved.

We have already described the most simple way in which crystals may

be formed, and we may easily make objects for our microscope in

this manner of all the substances we can find which are soluble in

water. With some we shall find that crystals do not form easily, in

which event we may modify our tactics and warm one drop of saturated

solution on the slide till nearly all the moisture is driven off, then

there should be no difficulty in watching the crystals in process

of formation. Common salt, sugar, alum, borax, washing soda, iron

sulphate, called also green vitriol and copper sulphate, or blue

vitriol, are common and easily obtained substances, all soluble in

water. As we carry our experiments a little further we shall find that

crystals formed from cold solutions as suggested in our first method

differ from those formed from hot solutions. Again, if we use some

other substance than water as our solvent the crystals which separate

out will differ once more. Many very interesting experiments may be

tried on these lines.

Many beautiful crystals may be obtained by dissolving various

substances in gelatine or gum. The method is simple. Gently warm

a little gelatine, to which is added an equal volume of water, in

a chemist’s test-tube. When the gelatine has all dissolved make a

saturated solution of the substance, from which crystals are derived.

Green or blue vitriol are good subjects for the experiment. Add a

little of the saturated solution to the gelatine and stir with a glass

rod, taking care to avoid the formation of air bubbles. A little of

the mixture may now be placed in a thin film on a slide covered with a

cover slip and left to cool. Examination when cool under the microscope

will show lovely fern-like crystals, whose beauty rivals that of ice

crystals familiar to us on our window panes during hard weather in the

winter. Barium chloride also produces very beautiful fern-like crystals

when treated in this manner. Chlorate of potash, familiar to most of

us as a remedy for sore throat, forms crystals totally dissimilar to

those substances we have named. Having made as many crystals as we wish

from water and also from gelatine solutions, we may turn our attention

to gum arabic. The method of obtaining crystals from this substance

is exactly similar to that described for gelatine except, of course,

that we substitute gum for gelatine. This work is of the greatest

interest, for not only does it yield wonderfully beautiful objects for

our microscope, but it is a hobby full of surprises. When we are about

to examine a new crystal for the first time we can never so much as

hazard what shape it will assume. Sugar, it may be mentioned, does not

crystallize at once from a saturated solution in water, and the best

method of obtaining the crystals is to warm the slide, on which we have

placed a drop of solution, and then when dry to set aside for a day; at

the end of that time, especially if the air be moist, the crystals will

have formed.

We shall find it interesting to try experiments in mixing two different

substances, then we shall probably obtain crystals totally unlike those

of either of the ingredients. As an example of this method, let us

make a saturated solution of a mixture of blue vitriol and magnesium

sulphate in water. Place a drop of the solution on a slide, heat over

a flame, not only till dry, but till the substance left on the slide

begins to melt. We must use every care not to crack the slide, and this

may best be accomplished by keeping it moving while over the flame.

Now if we watch our object through our microscope we can witness the

formation of wonderful feathery crystals, as the slide cools.

Some strikingly beautiful results may be obtained in another manner;

the method is used by analysts in their so-called fusion tests. We

take a small grain of some substance, say, lead nitrate, place it in

the centre of our slide, cover with a cover slip, and warm over a

flame till it melts. Then, taking a similar-sized grain of another

substance, such as saltpetre, we place it against the edge of the cover

slip on the side opposite to the lead nitrate. Further warming will

cause the saltpetre to melt, and run below the slide and mix with the

lead nitrate. If we watch the meeting of the two chemicals a wonderful

sight will reward us. The lead compound forms a “beautiful crystalline

skeleton,” whilst the saltpetre forms six-sided stars at the opposite

side of the cover slip. The experiment may be repeated, using lunar

caustic and saltpetre, also the iodides of silver and potassium; in

fact we may try any chemical substances we have at hand, though we

shall find that some do not melt very easily, and potassium chlorate

is somewhat dangerous, for it forms explosive compounds with certain

substances.

The number of interesting and beautiful objects which may be obtained

by so-called solution tests is practically unlimited, and the

enthusiastic microscopist will certainly try all the tests we describe

as well as many others of his own invention. Should the chemist wish to

detect the presence of aluminium in very small quantities, he relies on

his microscope and proceeds in the following manner. He takes a drop of

the solution, suspected of containing alum, and adds to it a drop of

sulphuric acid. This mixture he puts on his slide, which he heats over

a flame till dry. Now he adds a drop of water, and then a very small

amount of calcium chloride is brought to the edge of the water. Beneath

his microscope he can now watch the formation of beautiful colourless,

eight-sided crystals which denote the presence of aluminium.

A word of warning is necessary concerning this and the following

experiments; they may not always succeed, for success largely depends

upon having the solutions at the right strength, and experience alone

can teach us what is correct. Interesting and easily formed crystals

may be obtained from barium sulphate, and the experiment may also be

made to show the phenomenon which we have already mentioned, that the

form of the crystals depends on the nature of their solution. A little

barium sulphate should be dissolved in strong sulphuric acid. Here, by

the way, another warning: every care should be taken in the use of all

acids; they should never be allowed to come into contact with face,

hands or clothes, nor should they touch any part of the microscope.

Some acids give off fumes, and these should not be allowed to reach

the eyes or nose, and the microscope must be protected from them. To

continue our experiment: While hot a drop of the solution of barium

sulphate in sulphuric acid should be transferred by means of a glass

rod to a slide and allowed to cool. Examination with the microscope

will show that the barium sulphate has formed small rectangular

scales. With the remainder of the sulphuric acid we now make a

saturated solution of barium sulphate, and find, on repeating the

method described above, that the chemical has formed curious x-shaped

crystals. Similar experiments may be tried with calcium sulphate with

the certainty of interesting results.

Many crystals of calcium, in the form of calcium oxalate, may be

found in plants, and they are well worth looking for. They may best

be seen in sections of the plants, but, if we have not mastered the

art of cutting sections, we may find them by teasing the plant cells

apart with our mounted needles. In the stems of rhubarb there is the

substance in bundles of long needle-shaped crystals, to which the name

of raphides has been given. In the seed of the garden poppy, just below

the skin, there is a layer known as the crystal layer, where crystals

of calcium oxalate occur as tiny balls called crystal sand. In the leaf

stalks of begonias very beautiful and occasionally very large crystals

of this substance may be found, whilst in shapes they are strikingly

varied. In orris root there are enormous crystals of calcium oxalate;

in fact it is common in many plants.

If we have a photographic friend who will supply us with quite a small

quantity of gold chloride, we shall be in a position to try three most

interesting experiments and to obtain some curious crystals. We require

a very weak solution of gold chloride in water, not more than 3.5 per

cent. for our first experiment. Mix one drop of this solution with the

same quantity of hydrochloric acid on a slide and heat over a flame

till dry. The microscope will now show us probably the most curious

crystals we have ever examined; some are long, some short, and some a

zigzag in form; mixed with these there will be a few flat plate-like

crystals with rectangular projections. All these curious crystals are

yellow.

If instead of hydrochloric acid we use a solution of common salt in

water and repeat the experiment as before, we shall obtain pale yellow

prisms and some crystals of common salt. Gold is costly, so it is

perhaps lucky that one of the tests for this rare metal is one of the

most delicate known to chemists; it is possible, in fact, to detect

very minute quantities of gold. For this experiment we may take an

exceedingly weak solution of gold chloride and place a drop on our

slide; we also require a solution of the chloride of tin, known as

stannous chloride, in an evil smelling liquid called chlorine water. If

now we watch our drop of gold solution under the microscope, and while

watching mix with it a drop of stannous chloride solution, a strikingly

beautiful purple colouration is produced--this purple has been named

the purple of Cassius.

[Illustration:

_By the courtesy of Messrs. F. Davidson & Co._

1. THE EYE OF A COCKCHAFER

This section shows the eyelashes, the convex lenses, and, in the

lower portion of the plate, the nerve fibres leading from the brain

to the eye.

2. HOOKS ON BEE’S WING

The row of hooks on the margin of the bee’s wing are clearly shown.

By their aid the fore and hind wings are fastened together when the

insect flies.

]

If we desire further experiments in the testing of common substances,

and incidentally in the production of beautiful crystals, we might do

worse than try the effect of adding a solution of platinum chloride to

any solution containing a compound of potassium. Charmingly beautiful

crystals will result.

The experiments we have described as well as hundreds of others are

used by analysts every day in the testing of various substances. We

have started in every case by knowing what our solutions contain; the

duty of the analyst is to discover what he has before him. Given an

unlimited quantity of a substance for testing purposes it is not always

easy to determine its composition. With very small quantities, perhaps

less than a tea-spoon full in all, the difficulties of the analyst

are increased tenfold and without the assistance of the microscope

his efforts would be unavailing, he deals in drops and every drop is

precious. Sad to relate this form of testing, known to science as

micro-chemical analysis, has been practised to a far greater extent on

the continent than in this country.

Those of our readers who wish to try the experiments we have described

for themselves can obtain all the necessary substances, except the

poisons, at any chemists and the quantities required will only be the

smallest that can be obtained, in fact any reasonable-minded chemist

would probably let a microscopist whom he knew have a few grains of a

large number of chemical substances, suitable for this work, at the

outlay of a few pence. The chlorides of gold and platinum we fear no

one will give away.

All the experiments we have described thus far have necessitated the

use of what are called inorganic substances, they may be described in

every day language as substances derived from the inanimate world.

There are many equally interesting tests which may be carried out with

animal and vegetable products.

Formic acid is the substance which renders the sting of ants so

painful; it may, however, be prepared artificially and if a little,

dissolved in water, is mixed with a solution of silver nitrate we shall

obtain flat plate like crystals also some resembling fine fibres.

Probably the most curious of the easily obtained crystals from

vegetable products, may be made from citric acid which occurs in

lemons. If a little of the acid be mixed with a solution of caustic

soda and boiled with calcium chloride, a drop of the liquid after

boiling placed on a slide will give crystals readily. When viewed from

above they are an elongated oval shape, described by some authorities

as resembling a whetstone. Viewed from the side they have a striking

similarity to small sheaves of wheat.

With the recognition of poisons under the microscope we need not

trouble ourselves here. It would be useless to describe any of the

experiments, for few of us could obtain such deadly substances as

nicotine, strychnine, aconite, morphia and the like. Nevertheless the

recognition of these and similar substances in very minute quantities

is rendered easy, to those who have the necessary knowledge, by means

of the microscope.

CHAPTER XIX

THE USE OF THE MICROSCOPE IN MANUFACTURES

In how many branches of commerce, we wonder, does the microscope

play its part. It is used in several departments of engineering for

examining steels and many other metals not only for defects but to

see how they are made up. It is used in brewing for studying the

various yeasts and other substances, including the hops which go to

the making of beer. All manufactures which depend upon fermentation,

such as wine and vinegar making, are largely dependent upon the work

of the microscope. In dairy work the microscope is invaluable. In the

examination of various fabrics the assistance of the microscope is

always summoned. Paper manufacture and paper testing give work for

the microscopist but it would, we think, be easier to give a list of

the branches of commerce in which the microscope is not used than to

attempt to enumerate those which make use of the instrument.

We cannot possibly describe all the uses to which the microscope is

put, so we will confine ourselves to one or two of the more important

and, at the same time, to those which can, for the most part be

repeated at home.

The two most important commodities for mankind are food and clothing;

we cannot live without food and those of us who take but little pride

in our appearance, must have clothing of some sort. We have said a

little about food in another chapter and there we have also mentioned

the impurities which find their way, by accident or design, into some

of the commoner foods.

In this chapter we will deal first of all with clothing describing

how many of the raw materials may be recognised under the microscope

and showing very briefly how fraud in connection with the manufacture

of wearing apparel is detected. Practically all clothing is made from

animal or vegetable fibres, some, however, is made of artificial fibres

and these we shall mention.

The vegetable fibres used in the manufacture of wearing apparel are

all either hairs or what are called bast fibres and the latter, in

non-scientific language, may be described as the strands which run

through the roots and stems of most plants. The chief requirements of

vegetable fibres, destined to be woven into fabrics, are strength, it

is obvious that a weak fibre would be useless; length, the longer the

fibre the better and as we shall see later, short fibres are often made

up into inferior material; pliability, a stiff fibre would make an

uncomfortable fabric; firmness and durability. Animal fibres used in

the manufacture are either hairs or silk.

The most important vegetable fibre is cotton, it consists of the hairs

from the seed coats of several species of _Gossypium_, a plant closely

related to our common mallow. There are very many different kinds of

cotton and the qualities of the fibres of these different cottons vary

tremendously. Each hair is one cell and more or less spindle shaped,

that is to say, thicker towards the middle than at the base. If we

can obtain a little raw cotton we should certainly examine it under

the microscope; this may best be done by laying one or two fibres in

a drop of water on a slide. Under the low power, the first thing that

will attract our attention is the fact that the fibres are twisted,

corkscrew fashion, though not regularly nor throughout their whole

length. This curious twisting makes raw cotton easily recognised and it

is, at the same time, a very valuable peculiarity of these plant hairs.

The greater the number of twists and the greater their regularity, the

more valuable the cotton becomes for weaving purposes. Under a higher

magnification, we recognise other characteristics of the cotton fibre.

Each fibre is somewhat flattened, its edges are thick and, running up

the centre, there is a fairly broad lumen, as it is called. Covering

the whole there is a skin which by the way is often wanting in the

fibres of cotton fabric owing to the chemicals with which the raw

cotton has been treated and also to the methods of manufacture.

A very striking experiment may be tried by soaking a few cotton fibres

in cuprammonia, a substance prepared by the action of ammonia solution

on copper filings. Constrictions occur at fairly regular intervals

along the fibre so that, after treatment with cuprammonia, the cotton

fibres resemble strings of little beads.

The manufacture of mercerised cotton has become very important of late

years. The process is named after its inventor, Mercer, and consists

in removing the skin from the fibres, causing them to untwist and, by

doing so, to impart to them a lustre of silk. We may make a little

mercerised cotton for examination under the microscope by soaking some

raw fibres for a short time in a solution of caustic soda or caustic

potash and then washing them in water to which a little acid has been

added. This will cause the fibres to untwist and also destroy the

skin, but we shall probably notice that the fibres have shrunk. In the

process of manufacture precautions are taken to prevent this shrinking

for then the lustre is much better. We shall also observe that in our

mercerised fibres the lumen has become very narrow and it is often

broken, here and there are swellings on the outside of each fibre,

corresponding to the positions of the twists. Mercerised cotton, in

addition to its lustre, is stronger and absorbs dyes more easily than

ordinary cotton.

Flax consists of the bast fibres of the flax plant. Examination

of the raw product under the microscope will reveal both long and

short fibres. The former are the more valuable and are used in the

manufacture of linen, the latter are made into tow. The long fibres,

which are derived from the upper parts of the flax plant have thickened

edges and a very small lumen. The short fibres, used for making tow,

come from the lower part of the stem and the roots of the plant. Each

fibre has a broad lumen and is very similar to hemp fibre. Examination

of all these fibres, by the way, is best made in water as described

under cotton.

Hemp is another bast fibre and as we have remarked it resembles the

short fibres of flax; there is a broad lumen with an indistinct

margin. If we have an opportunity of comparing these fibres under the

microscope we shall see that many of those of hemp have forked ends.

This is very characteristic of the plant and is never found in flax,

therefore it affords a ready means of distinguishing hemp from flax.

Fine linen should never contain hemp, so that if our object be to test

the quality of a sample of linen by microscopic examination, we must

keep a sharp look out for the forked fibres of hemp. In coarse linen

these fibres occur for hemp is used in its manufacture.

Jute, another important fibre is readily distinguished under the

microscope, for its margins have perfectly smooth walls and its lumen

is wide in some places, narrow in others and interrupted altogether in

places.

[Illustration:

_Photos by Flatters & Garnett_

A SPIDER’S FOOT

The toothed claws are well adapted to enable their owner to obtain

a firm grasp of the fine threads of its web.

THE FOOT OF A FLY

The two claws enable the fly to walk up rough surfaces, whilst the

suckers between the claws give it a firm hold on smooth surfaces.

]

There are an extraordinary number of vegetable fibres which are woven

into articles of commerce, of one kind and another. Then again, many

fibres are so short or so brittle that they cannot be woven but are

used for other purposes such as filling cushions, cheap bedding, etc.

There are also a certain number of vegetable fibres which are valuable

because they are stiff and bristle-like as well as durable, and they

are used for brushes, door mats and for similar purposes. To the

microscopist who is interested in this work there is a wide field open.

For the examination of paper, which may be described as a “felt of

finely divided fibres,” the microscope is invaluable. The essentials of

a good paper are that it be durable, that it retain its colour and not

become brittle. The least observant of us cannot fail to have noticed

that there are an extraordinary number of different kinds of paper,

not only the many kinds which the paper manufacturers could show us,

but the obviously varied papers which we meet with every day. Added to

the papers, there are cardboards which are really a kind of paper. It

is clear, therefore, that the man who can tell us exactly how any and

every paper is made and what it is made of has laid up a goodly store

of knowledge. In carrying out tests of paper we rely partly on chemical

and partly on microscopic tests.

A number of substances contribute to the manufacture of paper; linen

and cotton rags, hemp and various fibres are the most commonly used,

not forgetting wood pulp which we shall mention in a moment. The

finest and whitest paper is made from linen rags and that from unused

linen and hemp is the strongest. Without attempting to describe in

detail or even in outline the different processes which the various

vegetable fibres must undergo before they appear in the guise of

paper, we may say the treatment is very drastic. Strong chemicals and

machinery designed to reduce the fibre to the finest possible particles

render the examination of paper, for the purpose of discovering its

composition, far from easy. Such fibres as survive the rough treatment

are mere fragments yet they are often large enough for the lynx eyed

microscope to read their story. Formerly the constituents of most

papers could be separated into three classes according to their

behaviour with iodine solution, but this test has been superseded by

more complicated methods which do not concern us here.

The examination of various papers may prove interesting for example in

linen rag paper, we ought to find some flax fibres, they will be sadly

battered and torn but are usually recognisable under the microscope.

Hemp paper is tough and is used for bank notes, in it some of the

short tow fibres will probably occur and they will give a clue to its

composition. Cotton rag paper is easily recognised for the fibres are

very characteristic, a remark which also applies to jute paper, the

so-called manila used for envelopes, wrappers, etc.

Mechanical wood pulp which enters so largely into the manufacture of

paper is easily recognised by those who have given a fair amount of

attention to the microscopical examination of plant life. Wood pulp is

always used in conjunction with some binding material such as cotton

or flax fibres. Many different kinds of wood are converted into pulp

and of course it requires a considerable amount of experience to say

exactly what kind of wood has been used in a certain paper. Some of

the woods are poplars of various kinds, others spruces and firs. It is

easy to distinguish the conifers as spruces and firs are called, for

the reason that the trees bear cones. The little fragments of wood,

scattered throughout the paper, have minute circular perforations upon

them, resembling miniature quoits, if they belong to the conifers; none

of the other woods possess these “pits” as they are called.

Very many other plant remains may be found in paper, for instance

hop fibres are used sometimes and their presence is usually shown by

remnants of the climbing hooks which, during life, studded the climbing

stem of the hop.

Some of the important animal hairs, used in the manufacture of

clothing, may now claim our attention. Wool and silk are of course the

most important. The best wool is all obtained from the domestic sheep

so let us examine one or two of the easily obtained hairs from this

animal. As with the vegetable fibres we may examine them in a drop of

water but, in this case, we shall find that we cannot make the water

go near the wool for the reason that the latter is covered with a film

of grease, called wool fat. Our first care, therefore, it to get rid of

the wool fat and this may be done by shaking the specimen with a little

ether or chloroform.

Having cleaned the wool fibres we may proceed to examine them under

a high magnification and, to see their structure fully, we must move

the fine adjustment to and fro, for it is not possible to obtain a

true idea of its structure without doing so. We shall see that the

hair consists of two layers, an outer skin and an inner core. The

latter consists of a number of cells, whilst the former is composed of

scales, of which the lower edges are arranged beneath the upper edges

of the previous scales, like tiles on a roof. The free edges of the

scales project outwards a little so that the wool, when not so highly

magnified, appears to have a toothed margin. Further examination will

show us that no single scale completely envelops the strand of wool,

usually two scales make the complete circuit. It is a curious and

easily tested phenomenon that in say an inch of wool from the same

kind of sheep there are always the same number or very nearly the same

number of scales. By counting the scales, experts can tell from what

animal the wool is derived.

If we examine many samples of wool we shall not be long before we

encounter certain specimens showing one or more constrictions. Now we

all know that the reason why some people do not grow very much is

because they are delicate, ill health affects the whole system. The

constrictions in the sheep’s wool occur because the animal has suffered

from some illness, or from great hunger or thirst, which has resulted

in its wool not growing properly for a period corresponding to the

duration of the illness or other calamity.

The examination of various animal hairs will help to while away many

an hour and many of these objects are of the greatest interest. If we

have the opportunity it will be interesting to compare the wool from

different kinds of sheep, that from the Lincoln sheep, for example

differs from that of shortwooled kinds. We may also compare goat’s wool

with sheep’s, then there are differences between the hair of cows and

calves. Comparisons always make microscopic work more interesting.

The microscopic examination of cloth, used for making our coats, is

quite interesting work and withal important. A good deal of the cloth

which is made up into suits is known as shoddy, that is to say that

material that has been worn before; old rags of all sorts and many

other extraordinary things go to the making of this cloth. There are

special factories to which rags are sent to be made up into shoddy. One

might think therefore that this substance would be easily recognised

under the microscope but it is not quite so easy as we shall see.

Absolutely pure wool from the sheep giving the best quality wool is

only used in the very finest and most expensive fabrics. In a great

deal of really good cloth we may recognise other hairs besides those of

the sheep and sometimes vegetable fibres find their way into good cloth

by accident. A piece of suspected cloth should be cut off and separated

as far as possible into its different fibres. In shoddy we shall find

few long fibres and they will all be much torn for the reason that the

rags from which the material is made are cut up in the manufacture. If

we find cotton fibres, we may be certain that our specimen is shoddy,

also if we can find fibres of many different colours, though the final

dyeing may have disguised the fact that the fibres have originally

figured in fabrics of various colours.

Silk is one of the most important of all fibres capable of being woven

into fabric. It is hardly necessary to remark that it is formed by

the fully fed silkworm just before it turns into a chrysalis. A very

large number of caterpillars spin silk but the majority of this silk is

useless for commercial purposes. The silkworm gives off a double thread

of silk from glands in its mouth and, at the same time, it gives off a

sticky substance called silk glue which sticks the two fibres together,

so that, to the eye at least they appear as one fibre.

Most of us have kept silkworms, those who have not may find it worth

while to expend a few pence in some of these insects for the sake of

examining the raw silk. A cocoon, as the work of the caterpillar is

called, consists of three layers, an outer layer of floss, a middle

layer and a so-called layer (the inner layer) of parchment. Only the

middle layer is used in commerce, the floss is too fine and weak and

the parchment is so impregnated with silk glue as to be useless.

If we examine some raw silk, taken from the middle layer of a cocoon,

we can easily see the two parallel fibres of silk and the outer

wrinkled covering of silk glue. Now, magnifying our object more highly,

we shall see that each fibre is a solid rod, with a smooth lustrous

surface and without any sign of lumen or cell structure; the rods

too are continuous and this alone distinguishes silk from all other

fibres animal or vegetable. Two tests are worth trying for they are

characteristic of silk. On the addition of a little strong sulphuric

acid we observe that the silk rapidly dissolves, on the other hand, if

a few fibres are boiled in hydrochloric acid, the silk dissolves but

the envelope of silk glue remains unchanged and appears beneath the

microscope as a cracked and wrinkled tube.

The caterpillar of another moth spins coarser greyish coloured fibres,

which are spun into the well known Tussore silk. As with the common

silkworm these caterpillars spin two fibres and glue them together

with silk glue. In this case, however, under a high magnification we

shall notice that the fibres are marked with a number of very fine

lines running lengthways, whilst every now and then there are fairly

deep indentations. The former markings are natural to the fibres,

the latter are caused by one fibre being pressed against the other.

In countries where the production of silk is of great importance, the

microscope is not only pressed into service for examining the product

of these useful little insects, but also in keeping watch for a very

deadly disease which attacks the caterpillars. It is called “pebrine”

and the great scientist Pasteur, whose name is world famous for his

work on bacteriology, discovered that it was caused by a tiny fungus.

Artificial silk is an important article of commerce. It is made in

several different ways and of various substances. Some artificial silk

is made of collodion, some again is made of cellulose the substance

of which the cell walls of young plants is composed; gelatine is also

used in making this commodity. As a rule it is easy to distinguish

artificial from real silk, for usually the imitation consists of flat

fibres or at least fibres quite different to the smooth rods of real

silk. The iodine test is often sufficient indication, for with this

chemical true silk is coloured brown.

Space or lack of it does not allow us to describe how the microscope

may be and is applied to other manufactures, even the miller uses the

instrument, for it will tell him if his flour is of pure wheat, and in

this manner. He puts a little flour in a drop of water on a slide and

covers with a cover slip; then, for a moment or two, he rubs the cover

glass to and fro over the water and flour and examines his specimen

under the microscope. If his flour be of wheat, he will see fairly

stout spindle shaped strings, if it be of rye no strings appear, whilst

maize flour gives very small strings. These are called gluten strings

and wheat is very rich in gluten.

CHAPTER XX

THE MICROSCOPE AND CAMERA ALLIED

Photography is such a popular hobby in these days, that the enthusiast

who possesses both camera and microscope, is certain, sooner or later,

to wish to take permanent records of some of the beautiful objects

revealed to him by the latter instrument. The production of high-power

photo-micrographs, as the pictures of highly magnified objects are

called, can only be carried out by those who are skilled in the use of

both camera and microscope and are possessed of considerable patience.

There is nothing to prevent any amateur photographer who possesses

a bellows camera--box cameras cannot be used for this work--from

producing excellent low-power photo-micrographs, that is to say

pictures of objects less highly magnified.

It may be disappointing to learn that a microscope is not necessary

for this work. The requirements are, a camera which will open out to

a considerable extent and a short focus lens. Before we show how the

pictures may be taken, we must be quite clear what is meant by a short

focus lens. There are various ways of measuring the focus of a lens; in

the case of a single lens the operation is fairly simple, but single

lenses are made of one glass and most camera lenses are built up of

several pieces of glass, then it is much more difficult to measure the

focus quite accurately. For ordinary purposes and for our purpose, it

is only necessary to know the focus in round figures and to do so we

open up the camera and focus some distant object on the ground glass,

then the distance in inches from the back of the lens to the ground

glass will give us very nearly the correct focus, or as it is often

called focal length, of our lens. Suppose we focus on a church steeple

a mile away and then find that a space of five inches separates the

back of our lens from the ground glass, the lens is of five inches

focal length.

With a lens of such a focal length we shall require a camera with

very long bellows to obtain much magnification of our object but, if

our camera is one with only short bellows, we can still overcome our

difficulties. If the extra expense is no object we can obtain one of

the excellent Aldis lenses of only two inches focal length, especially

designed for this work; if we are ingenious we can construct a device

which will answer our purpose admirably and cost but a few pence. With

the simple apparatus we are about to describe photo-micrographs up to

ten diameters magnification can be obtained in most cameras. The term,

ten diameters, may appear puzzling but really it is quite simple.

Suppose we wish to make a photo-micrograph of a penny stamp and we wish

it to be magnified ten diameters, we should require a large camera

for the operation, but that, for the moment, is beside the point. Our

penny stamp, magnified ten diameters, would be equal in area to ten

horizontal rows of stamps, each row containing ten stamps or, in other

words, it would occupy the same area as one hundred penny stamps.

To find the magnification possible with our camera and lens, extend

the camera bellows to the full and set up a foot rule in front of the

lens. Move the camera from a distance slowly towards the rule till it

is sharply focussed, then carefully measure the distance between the

inch lines on the focussing screen; if the lines are three inches apart

we shall be able to make photo-micrographs three times the size of our

object and we shall probably desire something better.

To obtain a considerably magnified picture we must have a lens of short

focal length and a camera with long bellows, in fact in theory the

amount of magnification is only limited by the length of the bellows,

so that an extraordinarily long camera should give us a much magnified

picture. We cannot lengthen our bellows without considerable expense,

but we can shorten the focal length of our lens. If we obtain, at the

cost of a few pence, a convex lens of short focal length, such as is

used in cheap magnifiers we can easily apply it to our camera lens

and it will have the effect of shortening its focus. This extra lens

can either be fitted in front of our original lens by cutting two

inches of cardboard, of such a size that they will just fit into the

lens hood. In the centre of each piece of cardboard, cut two circles,

slightly smaller in diameter than the diameter of the convex lens.

Place the lens over the opening in one of the pieces of cardboard and

stick the other piece upon it with glue or seccotine. When dry fix the

lens in its cardboard holder in the front of the lens hood and repeat

the focussing experiment with the foot rule. We shall now obtain a much

greater magnification with the same length of bellows, because the

additional lens has shortened the focus of our original lens. Probably

our camera is fitted with a double lens and it is possible to unscrew

the front portion, in this event our extra lens with its cardboard

holder may be fitted inside the front lens up against the diaphragm and

the front lens replaced. The result is practically the same whatever

the position of the new lens, but we must be certain that it is convex,

for a concave lens would increase the focal length of the whole and so

reduce our magnification.

We may find that the amount of enlargement we can now obtain is

sufficient for our purpose; if so we can go ahead and produce

photo-micrographs of all the objects we desire. The methods of doing so

differ in no way from those employed in taking ordinary photographs and

as we are writing about microscopy and not photography in these pages,

there is no need to go into further details. Even the experienced

photographer, however, is liable to overlook one or two important

details. The bugbear in all work of this kind, with low magnifications

as well as high, is vibration. Not only is our object magnified but

every movement is equally increased. No one should walk across the

room while this work is in progress; in large towns, trams and heavy

motors will ruin many a plate, in fact it is only when one takes up

work of this kind that one realises that one’s house is in a perpetual

quiver. Some enthusiasts work at the dead of night, others suspend

their apparatus on springs and invent all kinds of ingenious devices to

overcome these miniature earthquakes.

If time is no object, we have an easy means of still further increasing

the magnification. To do so we cut a thin sheet of copper in such a

manner that it just fits our lens tube, in front of the diaphragm. Then

in the very centre of the copper disc we make a hole with a “number

one” needle, the hole is about one twentieth of an inch in diameter.

Replace the convex lens in its cardboard holder and screw on the front

portion of the camera lens. A trial will show that we have considerably

increased the magnification but decreased the amount of light admitted

by the lens, therefore we shall probably require an exposure as long as

an hour. How about the bugbear vibration during such a long exposure

is a natural question to ask. Unless the vibration is continuous, and

that is unlikely, it is less likely to cause trouble during a very long

exposure than during a short one, because it operates during a small

proportion of the whole time.

All kinds of objects can be depicted with the apparatus we have

described. Minute shells and insects; parts of larger insects, their

legs and wings for example; the feathers of birds; various rocks,

crystals of all kinds; small flowers and their seeds; mosses, lichens

and many kinds of fungus, in fact their number is limited only by the

degree of ingenuity possessed by the photographer. Do not suppose

that these low-power photo-micrographs are interesting only because

of their size, the enthusiast who makes a collection will discover

in his prints hidden beauty of which he had no conception when he

looked at the originals. We have seen a very large number of low-power

photo-micrographs, taken with very inexpensive apparatus, showing

the wonderful sculpturing on the wing cases of beetles, some of them

are marvels of design, yet, observed with the naked eye, many of the

insects appear to be devoid of ornamentation.

The production of high-power photo-micrographs is hardly a subject that

can be described in these pages; the apparatus is costly for, even if

one dispenses with a specially designed micro-photographic camera, it

is necessary to have a good microscope and bellows camera, for really

advanced work. Messrs Swift & Sons supply an excellent fitting, with

which quite satisfactory photo-micrographs may be taken. It consists of

a light metal cone, the more pointed end fits over the upper portion

of the microscope tube; the other end of the cone is provided with

ground and plain glass focussing screens and a dark slide. When using

this apparatus, it is first necessary to find and focus our object in

the ordinary way, before attaching the photographic apparatus. Having

secured our object exactly as we wish it to be depicted and well in

the centre of the illuminated circle, we remove the eyepiece and slip

the metal camera over the top of the microscope tube. If now we place

the ground glass screen in position, we can see an image of our object

upon it. Great attention must be paid to the lighting, it is necessary

that the illumination be perfectly even, otherwise our negative will be

over-exposed in some parts and under-exposed in others. When everything

is in order the plain glass screen is substituted for the one of ground

glass. On this we shall probably not see any image with the naked eye,

but with the help of a magnifying glass we can see a much finer image

than was possible on the ground glass screen. The final focussing is

done at this stage and, having secured as sharp an image as possible,

the focussing screen is removed and the exposure is made. Experience

alone will teach the length of exposure, it depends upon the amount

and nature of the light, upon the transparency of the object and

also upon its colour. There is no more simple apparatus for taking

moderately high-power photo-micrographs; for more advanced work the

micro-telescope and the super-microscope (see Chapter XVII) used with a

camera, will enable the user to obtain pictures of objects magnified as

much as five thousand times.

CHAPTER XXI

HOW THE GLASS USED IN MICROSCOPES IS MADE

Having described all the ordinary uses of the microscope and having

also insisted that the objectives are the most important part of the

instrument, there are probably many of our readers who may wish to know

in what manner this wonderful glass differs from ordinary glass and how

it is made.

Glass has been defined as a substance which, during its manufacture,

passes from the liquid to the solid state so rapidly that no crystals

are formed. Usually when solids are melted and then allowed to cool,

they do so with the formation of crystals, this may be shown in the

case of sulphur by melting a little and then allowing it to cool. After

a while, as cooling takes place a solid crust will be formed on the

surface of the molten sulphur. If two holes are pierced in the crust

and the still liquid sulphur poured out, it will be found that the

sulphur which adhered to the vessel in which the melting took place has

formed beautiful needle shaped crystals.

A great amount of original work has been done on the subject of glass

manufacture and especially on the kind used for optical instruments--as

a result there are many kinds of glass differing from one another in

physical properties and in chemical composition. Although the various

chemicals used and their proportions are fairly well standardised,

as the result of long experience, it is probable that glass is not

a definite chemical compound but a mixture, in which certain of the

components act as solvents for the rest.

The ordinary glass in use in this country, apart from specially

prepared optical glass, may be either English flint glass, plate

glass or Bohemian glass. The first named is composed of sand,

potassium carbonate and red lead; plate glass is made of sand with the

carbonates of sodium and calcium, whilst similar ingredients are used

for Bohemian glass except that carbonate of potassium is substituted

for carbonate of sodium. It is chiefly owing to the requirements of

optical instrument makers that, new kinds of glass containing very many

previously untried chemicals, have been produced. As a result glasses

are now made with specific gravities varying from 2.5 to 5.0, that is

to say the weight of a square inch, or a square foot or a square yard

of glass may weigh anything from two and a half to five times more than

a square inch, foot or yard of water, according to its composition.

Before we describe the details of its manufacture let us consider its

properties as briefly as possible. At high temperatures it is perfectly

fluid and may be poured from vessel to vessel as easily as water; at

lower temperatures it is viscous, _i.e._, semi-fluid and can be rolled

with an iron roller as dough is rolled with a rolling pin; it can be

moulded into any desired shape, blown out into flasks and bottles or

drawn out into threads so fine that they may be woven into a fabric. It

is a bad conductor of heat and for this reason it is safer to pour very

hot liquids into a thin glass vessel than into a thick one. With thick

glass the inner layers expand with the heat before the outer layers

are even warm and the result is a crack or often absolute fracture.

Sometimes during manufacture glass vessels which are suddenly cooled

will appear satisfactory, but the particles of glass remain in so high

a state of tension that at the slightest touch the vessel will break up

into thousands of pieces. On account of this property of glass it must

be cooled very slowly indeed; the process is known as annealing.

Optical glass unlike most other kinds must be manufactured in thick

blocks--some of the large lenses on telescopes are of considerable

thickness. All glass for scientific instruments must also be

homogeneous, which our dictionary tells us means of the same kind. To

be more explicit each particle of optical glass should be precisely the

same in composition and properties as every other particle. In the very

early days of manufacture it was difficult to obtain homogeneous pieces

of glass and Guinard, in the 18th century, conceived the idea of

stirring the molten glass with a rod of fireclay, to ensure a thorough

mixing of the components. This led to considerable improvement and the

method has survived to the present day.

The first real advance in the manufacture of optical glass, was due

to the ingenuity of two Germans, Abbe and Schott, who lived at Jena.

Jena glass became famous for the manufacture of lenses, so much so that

a stupid idea still prevails in many quarters that only the Germans

can make good optical glass. To give them their due it is good but

quite recent events have shown the world that the Britisher can make

better. The two German scientists used new chemicals in making their

glass and they succeeded in producing a substance which possessed

hitherto unheard of properties. In what is now known as the older

crown and flint glass the dispersion and refraction increased with the

density, that is to say, the heavier the glass the more it scatters

and bends light rays passing through it. With the new methods, glass

is made which scatters the light rays very little, though bending them

considerably and vice versa. The ordinary crown glass is composed

of silicates of calcium and sodium or of calcium and potassium or a

mixture of both and it is possible to make it colourless and free from

defects, but its optical properties are never so valuable as those of

Jena glass. The most important components of the newer glass are the

oxides of Barium, Magnesium, Aluminium, Zinc and Boron.

Good optical glass should be transparent and colourless and, as we have

stated, it should be homogeneous--the refraction and dispersion of

light rays should be identical over all parts of the glass. It should

possess no striæ, as they are called. Striæ may be seen at the edge of

a piece of plate glass as little lines just as though the glass had

been formed in layers. Striæ detract from the efficiency of optical

glass, nevertheless, some very cheap lenses are made of plate glass.

Bubbles are almost always present in Jena glass but, unless they are

very numerous they do not appear to render the glass less efficient.

Hardness and chemical stability are other desirable qualities. Most of

these high-grade glasses are soft, as shown by the ease with which they

may be scratched; many of them are not very stable chemically and are

easily affected by chemical fumes with the result that their surfaces

become covered with a coloured film. With all their drawbacks, for

optical work the newer glasses far excel the older.

The manufacture of optical glass is a costly and lengthy process.

The chemicals used in its manufacture are selected with the greatest

care; impurities must be guarded against for they would change the

composition of the glass and in doing so alter its physical properties

on which everything depends. The chemical substances are used either

in the form of oxides, nitrates or carbonates, for the reason that

they are easily decomposed by heat. To assist in the melting of the

substances a few fragments of glass of similar composition are added.

The crucibles, in which the chemical components are melted, are covered

so that no fumes from the furnace may gain access to them, even the

chemical composition of the crucibles is carefully tested that no

impurities may contaminate the glass. No crucible is ever used more

than once and only a single crucible is heated in each furnace, in

order that the temperature may be regulated to a nicety.

The actual manufacture is then begun after all these preliminaries have

been attended to. A clean dry crucible is heated in a furnace--not the

one in which the glass making is to take place--to a dull red heat.

Then, with iron tongs, it is removed to the previously heated glass

making furnace and the temperature is raised very gradually. The next

stage sees the addition of the well mixed chemicals to the heated

crucible, in small quantities at a time. When the full quantity has

been added the crucible contains melted glass full of bubbles, some of

them air bubbles released from the raw materials as they were added

and some bubbles of gas given off from the chemicals as they act upon

one another. The molten glass is then heated strongly so that it will

become perfectly liquid and many of the bubbles will be driven off. To

reach this stage may occupy anything from thirty-six to sixty hours and

constant attention is necessary during the whole time.

The next stage is perhaps the most important in the whole process.

After numerous small samples of the molten glass have been taken, on

the end of iron rods, to see if the air bubbles have been driven off,

the mixture is stirred to render it homogeneous and to eradicate striæ.

The stirring is carried out by means of a cylinder of fireclay which is

first of all heated to the temperature of the molten glass before it is

introduced. To the end of the fireclay cylinder a long, detachable iron

handle is fixed so that the man who undertakes the stirring may stand

at a distance from the hot furnace. The heat is great and the work of

stirring is laborious and for this reason the stirrers are constantly

changed. The iron handles must be watched carefully for, owing to the

heat they rust rapidly and should any of the rust fall into the molten

glass it would impart to it a colour and render it useless for optical

purposes. When stirring begins the glass is liquid as water, but the

stirring is continued during cooling and all the while the glass is

gradually becoming more and more solid. During the final stages the

operation is hard labour indeed and, finally, it is not possible to

stir any more, then the fireclay cylinder is either removed or left in

the glass.

When the glass has solidified and, whilst it is still hot the furnace

is sealed and allowed to cool very gradually till it has reached the

ordinary temperature of its surroundings; this may take several weeks.

When quite cool, the crucible is removed from the furnace and carefully

broken; then the glass, which may be in one mass weighing as much as

1000 lbs., is freed from particles of fireclay and examined for defects.

The next stage consists of moulding and annealing. Large pieces of

glass are heated till they are just soft, then they are passed into

iron or fireclay moulds designed so that the glass is formed into discs

or slabs suitable for grinding by opticians. They are allowed to cool

very slowly in the moulds.

When the glass is taken from the moulds it is not yet ready to be made

into lenses. It is subjected to another and very careful examination,

when all defective parts are cut out. Should there be many defects the

glass is again heated, moulded and annealed. From a crucible containing

1000 lbs. of molten glass it is unusual to obtain much more than 200

lbs. of optically perfect glass, it is obvious therefore that lenses

cannot be cheap.

One would naturally imagine that the minute lenses used in microscope

objectives should be cheaper in comparison than the larger lenses used

for photography or in telescopes, for it is always more difficult

to make minute articles than large ones. As a matter of fact, even

allowing for the greater amount of material used in the larger lenses,

quality being the same in both cases, they are far more expensive

than the smaller microscope lenses; the reason being that it is

exceedingly difficult to obtain a perfect specimen of large size. The

difficulty arises not only in the actual manufacture of the glass but

in the subsequent operations of cutting, grinding and polishing when

fractures are very liable to occur.

From this brief account of the manufacture of optical glass it is clear

that a good lens is always worth a high price. Its components must be

of the purest quality obtainable, the process of manufacture requires

highly skilled labour and it is laborious and exacting work. Constant

attention is needed from start to finish and much of the glass is never

sufficiently good to pass the rigorous tests which it must undergo.

Lastly, in the final preparations of the completed lens, mishaps are

frequent. Added to all these trials of the lens maker is the one

outstanding fact that the process can never be hurried at any stage,

the efficient annealing of optical glass is one of the most important

stages in its manufacture. A very full account of the manufacture of

optical glass is given in the _Encyclopædia Britannica_, whence much of

our information in this chapter is derived.

CHAPTER XXII

THE CHOICE AND USE OF APPARATUS AND ACCESSORIES

In this, our concluding chapter, we propose to give a few hints upon

the choice and use of the microscope and its accessories, to enlighten

our readers concerning stains and staining and to add such other

information as is likely to be useful, information which is better

supplied in a chapter of its own than scattered about our pages and

probably overlooked.

The most important question concerns the choice of a microscope. In

a book of this nature it is obviously impossible to recommend the

wares of any one maker. Some firms are celebrated for the good wearing

qualities of their instruments, some for the delicacy--not fragility by

the way--of their fine adjustments and our readers must select their

maker for themselves. One thing we strongly advise, be patriotic and

select a British maker, it is not only a question of patriotism but of

self interest, for in many respects the British instruments lead the

world. Most of the manufacturers advertise in such papers as _Nature_,

they all print excellent catalogues, a perusal of which may be a useful

preliminary.

The instrument we select will depend on the use to which we intend to

put it and on the length of our purse. Perhaps the question of cost

will be more important to most people. An elaborate instrument is not

a desirable acquisition, till we are somewhat advanced in our work

at anyrate, and one of the models which most makers call Students’

Microscopes will do everything we desire. We should have at least two

objectives, three if we can afford them, a 1 inch and a 1/6 inch will

enable us to examine everything described in these pages, except some

of the bacteria. If we wish to add a third objective we might select

a 2 inch one, for quite low-power work and later we shall probably

become the proud possessors of a 1/12 inch objective, but this would be

of little use to us at first. Two eyepieces will complete our optical

equipment. A condenser for the stage, properly known as a substage

condenser is an addition which we shall appreciate, though quite

interesting work may be done without it.

Our other apparatus is inexpensive and comprises, one or two dissecting

knives, some needles mounted in handles, a pair of fine scissors, a

pair of small forceps, a razor, one or two camel hair brushes, three

or four watch glasses, slides and cover slips, and a pipette or two. A

pipette, by the way, is merely a glass tube pointed at one end and cut

off square at the other; at about its centre it is much wider than at

the top or bottom. It is a most useful piece of apparatus for picking

up small water animals which we wish to examine. By putting the pointed

end of the pipette just over an _Amœba_, for example, and sucking

gently at the other end, we shall draw some water and the animal into

the swollen part of the tube. If we then place one finger over the end

of the pipette to which we have applied suction we can transfer the

contents wherever we wish without it running out, as soon as we remove

our finger the pipette empties itself. The dissecting knives are useful

for cutting up specimens before examination, the mounted needles for

teasing them, that is to say tearing them into fine shreds. The brushes

we may use instead of the pipette, for picking up small objects from

water, or when dry. The watch glasses are useful for examining objects

such as sponges, water fleas, etc., under water. They are just as

satisfactory for most purposes as the specially constructed zoophyte

troughs and, of course, very much cheaper. The razor is required for

section cutting concerning which we will say a few words.

For section cutting, special razors are sold, they are heavy as a rule

and not hollow ground. Many microscopists aver that good sections

cannot be cut with a hollow ground razor, we beg to differ, however.

On this point we would advise our readers to select whichever pattern

suits them best; there is no need to buy an expensive razor, for our

early efforts, at anyrate, will quickly dull the cutting edge and

there is no advantage in going to much expense in this direction.

To cut really good sections is not difficult, it is a question of knack

rather than skill; having once acquired the knack, practice will do the

rest. The great point is to begin properly, some people never take the

necessary trouble in their early days and, as a consequence, they never

learn to cut good sections.

There is nothing mysterious about the operation, a section is merely a

very thin slice. A good section for examination under the microscope

should, of course, be so thin that it is transparent; it should be

equally thin everywhere, not thick in some places and thin in others

and it should be cut in the proper direction. The last statement

requires a little explanation; suppose we wish to make a section

straight across a stem, a transverse section it would be called, then

we must see to it that our section is cut straight across, and not in

such a manner that the portion from which the section is cut tapers

in the slightest degree. Before we begin the actual section cutting

we must always trim up our specimen with one of the dissecting knives

and not attempt to make the surface level with the razor. As a start,

let us take some moderately fleshy plant stem for we shall find it as

easy to cut as anything. Our stem must not be woody, for till we have

had a fair amount of practice we shall damage our razor on its hard

structures; it must not be too soft or it will be crushed out of all

recognition in our fingers; it should not be hollow, for solid stems

are always easier to cut. Having selected our stem and the spot upon it

at which we require a section, we cut straight across it at that spot

with our dissecting knife, in such a manner that the cut edge is as

nearly as possible at right angles to the sides of the stem. A piece

two or three inches long is the most comfortable to hold.

Holding our razor firmly in the right hand we take our specimen in the

thumb and index finger of the left hand. Place the side of the stem

against the first joint of the index finger and slightly bend the tip

of the finger round the object. The end of the stem, from which we

propose to cut our section, should be slightly above the level of the

index finger. With the thumb, the stem is pressed firmly against the

first joint of the index finger and the first joint of the thumb must

not be bent upwards. This last point is very important, as we shall

see in a moment. From our description the method of holding the stem

may seem somewhat cramped; it should not be so, however, and an easy

position will help towards success but let it be the correct position.

We may play the violin, in a manner, without learning the correct

method of bowing but we can never become expert violinists unless we

hold our bow properly, in the same way we can never cut really fine

sections unless we hold our specimen in the correct way. We now lay our

razor along the second joint of the index finger in such a manner that

the heel of the razor, or a point near the heel comes gainst the end of

the stem. For the first time we realize the importance of holding our

specimen correctly, for the index finger forms a convenient platform

on which to steady the razor. To cut our section, we, of course, press

the razor towards us and, at the same time draw it outwards from heel

to toe. We must never attempt to press the razor straight through the

specimen, however soft the latter may be, we must always draw the razor

along, at the same time as we press it through the specimen. Never cut

outwards as in sharpening a pencil and never move the razor backwards

and forwards as though using a saw. The outward cut will never result

in a good section, a sawing movement will give a section alternately

thick and thin. Should the section be somewhat tough we may find the

razor slip suddenly over its surface, an event which will impress

itself upon us painfully if we have forgotten the injunction not to

bend the thumb, for the certain result of the slip will be the loss of

a goodly portion of skin upon one’s joint. A straight thumb will be out

of the danger zone of a slipping razor.

[Illustration:

_By the courtesy of Messrs. F. Davidson & Co._

1. A FLY’S EYE

A fly’s eye highly magnified, showing some of the many lenses of

which it is composed.

2. IMAGES SEEN BY A FLY

Photographs of a statue taken through a fly’s eye. Instead of

seeing one image of an object, the fly sees as many images as there

are lenses in its eyes.

]

Having cut a section it is hardly likely that, at this our first

attempt, it will be good enough to put under the microscope, so we

will continue to cut section after section till we have a dozen or

more from these we can select the most transparent for examination.

The sections of such material as a stem should be kept moist and

to do so we will place them in a watch glass containing water. It is

often easier, also, to cut our sections if the razor be moistened with

water, at anyrate the moisture prevents the sections from adhering to

the razor. The sections should be removed from razor to watch glass

and from watch glass to slide, by means of a brush, never by means of

the fingers. The razor of course, should be well dried with a soft rag

before it is put away; rust, besides being unsightly, ruins the cutting

edge. If we are really anxious to cut our own sections, and every good

microscopist does so, we shall return to the operation again and again,

even cutting objects which we have no desire to examine, for the sake

of the practice. We shall soon reach a stage where our razor will be

dulled and require stropping and the efficient stropping of a razor is,

to many people, a more difficult operation than the cutting of sections.

We may point out here, that all sections are not quite so easy to cut

as the one we have taken as our example. Some objects are so soft that

they need hardening with chemicals before they can be cut, some are

so hard that to attempt to cut them would ruin the edge of the razor,

though it is wonderful what hard substances may be cut when we have

had a little experience; some are so delicate that they must needs be

buried in melted wax, then object and wax are cut together and later

the wax is separated from the section.

Leaves and very small stems may be sectioned by the beginner, as

easily as larger stems. For such objects little sticks of pith are

sold as holders. Having cut of our piece of leaf from which we wish to

derive a section, we make a slit, with our dissecting knife, down the

middle of one end of a piece of pith. The piece of leaf is then placed

in the slit and by holding the pith at the sides our piece of leaf is

held firmly. Sections are cut through pith and leaf, and the two are

floated in water, when the thin slices of pith will float away from the

leaf sections.

Having cut a satisfactory section, let us proceed to describe the

method of making a slide thereof. We will suppose that we do not

wish to make a permanent preparation but one for temporary use. A

clean slide must be selected, all through our pages we emphasise the

cleanliness of slides, at or near its centre we put a drop of water

and, lifting it with a brush, we place our section in the drop of

water. If our examination is to be with a low magnification, we need

not use a cover slip, nevertheless it is worth while to cultivate the

habit of using one. The cover slip is not only a protection for our

object but for our objective. Water you may argue cannot harm the

lenses of the objective. Perhaps not, we will not argue the point but,

when the water dries on the objective, it leaves a certain amount of

deposit on the glass and this deposit must be rubbed off. The less

often the lenses are rubbed the better for them, glass especially very

highly polished optical glass, is far more easily scratched than many

people imagine and a scratched lens is an inefficient lens. When using

high magnifications a cover glass should always cover our object and

the same remark applies to objects examined in Canada Balsam. This

substance is likely to cause serious trouble if it finds its way on to

an objective. It must be removed, that is obvious, but it sets hard,

it must not be scraped away for fear of damaging the optical glass

and, as it is used to cement the lenses together, there is the great

danger that any solvent used to remove the Balsam from the face of the

objectives, may also dissolve their setting. Our digression may seem

somewhat unnecessary, but the very great importance of keeping all

chemicals and even water, from coming into contact with the lenses of

our instrument cannot be insisted upon too strongly.

In whatever substance we examine our object, water, glycerine or

Balsam, there is a right and a wrong way of applying the cover slip. It

must not be dropped or laid down flat upon the object, if we do this

we shall certainly imprison a number of air bubbles and that must be

avoided. One edge of the cover slip must be laid against the edge of

the mountant, as the liquid used for mounting our object is called,

then placing a needle beneath the cover slip it must be gently lowered

into position. We shall now find that all air bubbles are driven out as

the cover slip is lowered.

When we have cut an exceptionally good section or when we have some

specially interesting object we may wish to make a permanent slide.

The exact method of doing so varies somewhat with the nature of our

object and to describe all the methods of mounting microscopic objects

permanently would require a book in itself. We will suppose that we

wish to make a permanent slide of one of the sections floating in

our watch glass of water. The first thing we must do is to get rid

of the water with which our section by now is saturated. This may be

accomplished by means of alcohol of various strengths, which we may

put into three watch glasses. In the first watch glass we have half

pure alcohol and half water; in the second three-quarters alcohol and

one part water; in the third watch glass pure or absolute alcohol. The

section is transferred on a brush to the first watch glass and left

there for five minutes, then to the second watch glass for a similar

time and finally to the third watch glass. The mountant may be either

Canada Balsam or glycerine jelly. Should we decide on Canada Balsam,

we put a small drop of the substance in the centre of a clean slide,

place one section atop of it and then gently lower a cover slip upon

it as already described. Then, without using any force, the cover slip

is pressed down, but we must not fall into the all too common error of

thinking that a thick section can be made thin by pressing upon the

cover slip. If we have taken the correct amount of Canada Balsam it

will just cover the area below the cover slip and no more, if we have

used too much, it will flow out on all sides and perhaps on the top of

the cover slip. A very little experience will teach how big a drop of

Balsam to use.

Should we decide to use glycerine jelly, we take a small globule of

the jelly on one of our mounted needles and place it in the centre of

a clean slide. Then we hold the slide a little above a lighted candle,

or even a match will do, to melt the jelly. Directly it is melted

the section is placed upon it, and we proceed as before. Whichever

mountant we have used, the slides must be put away out of the dust, and

they must be flat and not placed on edge. In a few days the mountant

will set, and we need take no further precautions with the slides in

which Balsam was used, but those mounted in glycerine jelly must be

ringed, for the reason that glycerine absorbs moisture from the air and

gradually liquifies.

The process of ringing is best performed upon a turntable, which any

dealer in microscope accessories will supply. It consists of a circular

brass plate which revolves about its centre and to which the slide to

be ringed is affixed. A bottle of ringing asphalt and a fine paint

brush are essentials. With a little of the asphalt upon our brush, we

revolve the turntable and place the brush against the edge of the cover

slip as it revolves, in such a manner that we paint a narrow rim of

asphalt over the junction of cover slip and slide. The asphalt prevents

moisture from reaching the glycerine jelly. Of course we may ring our

slides without making use of a turntable, but it is not easy to paint

a neat ring without mechanical assistance. For square cover slips it

is obvious that a turntable is useless. Specimens mounted in Canada

Balsam do not need ringing, for the Balsam is unaffected by air or the

moisture therein, when once it has set hard.

Several firms supply prepared microscope slides, and it is often

useful to know where reliable preparations may be obtained. The

slides supplied by Messrs Flatters & Garnett Ltd., 409 Oxford Road,

Manchester, are models of what well-made slides should be.

It always lends greater interest to the hobby if objects are found and

mounted by the microscopist himself. By going out into the fields, by

the pond-side, or along the shore, in search of interesting material

for examination, much will be learned of animal and plant habits which

even the microscope cannot reveal. Some of us, however, have neither

the opportunity to hunt for our specimens, nor the time to mount them

properly, and those of us who are so situated will be glad to know

where objects may be obtained.

Apparatus, useful for students of pond or sea-shore life, may be

obtained from Messrs Flatters & Garnett, who always have a goodly stock

of collecting jars, nets, &c. From the same firm, also, may be obtained

stains and any of the limited number of chemicals required by the

microscopist.

We have given a few simple directions for staining in our chapter on

Bacteria. In many cases it is absolutely necessary to have recourse to

stains in order to see the structure of the objects we are desirous of

examining; in other cases it is necessary to stain when we wish to know

the nature of the various parts of our object. Suppose, for example, we

wish to find out whether a plant section contains starch, we then add

iodine solution, and if any parts stain deep blue we know at once that

starch is present. There are other stains for other plant and animal

substances; stains for woody matter, stains for fats, &c., but the art

of staining is a science in itself, and would require many chapters

to describe fully. Most of the objects described in this book can be

studied in the natural state, but, even so, they may be rendered far

more beautiful by staining.