principal part the observer must aim at, in order to view the
circulation of the blood, is to procure those small animals or insects
that are most transparent, that by seeing through them he may be enabled
to discover the internal motion. The particular kinds best adapted for
the purpose will be enumerated in the descriptive catalogue at the end
of this work.
If a small eel be used for this purpose, it must be cleansed from the
slime which covers it; after which it maybe put either in the fish-pan,
or a glass tube filled with water, and then placed under the microscope.
If the eel be small enough, the circulation may be viewed in the most
satisfactory manner. Leeuwenhoeck has given, in his 112th Epistle, an
accurate description of the blood vessels in part of the tail of an eel.
The same figure may also be seen in my father’s Micrographia Illustrata,
fourth edition, Plate XVII. The tail of any other small fish may be
applied in the same manner, or tied on a slip of flat glass, and be thus
laid before the microscope. Flounders, eels, and gudgeons, are to be had
at almost any time in London. N. B. By filling the tube with water, when
an eel is used, it will in a great measure prevent the sliminess of the
eel from soiling the glass.
To view the particles of the blood, take a small drop of it when warm,
and spread it as thin as possible upon a flat piece of glass. By
diluting it a little with warm water, some of the larger particles will
divide from the smaller, and many of them will be subdivided into still
smaller; or a little drop of blood may be put into a capillary tube of
glass, and be then presented before the microscope. Mr. Baker advises
the mixing the blood with a little warm milk, which he says, will cause
the unbroken particles to be very distinctly seen. But the most accurate
observer of these particles was Mr. Hewson, and he says they have been
termed globules with great impropriety, being in reality flat bodies.
When we consider how many ingenious persons have been employed in
examining the blood with the best microscopes, it appears surprizing
that the figure of the particles should be mistaken; but the wonder is
lessened when we reflect how many obvious things are overlooked, till
our attention is particularly directed towards them; and besides, the
blood in the human subject, and in quadrupeds, is so full of these
particles, that it is with great difficulty they can be seen separate,
until the blood is diluted. It was by discovering a proper method to
effect this, that Mr. Hewson was indebted for his success. He diluted
the particles with serum, in which they would remain undissolved, and as
he could dilute them to any degree with the serum, he could easily
examine the particles distinct from each other; for example, take a
small quantity of the serum of the human blood, and shake a piece of
crassamentum in it, till it be coloured a little with the red particles;
then with a soft hair pencil spread a little of it on a piece of thin
glass, and place this glass under the microscope, in such a manner as
not to be quite horizontal, but rather higher at one end than the other;
by which means the serum will flow from the higher to the lower
extremity, and as it flows, some of the particles will be found to swim
on their flat sides, and will appear to have a dark spot in the middle;
others will turn over from one side to the other, as they roll down the
glass.
Several authors have described an apparatus for viewing the circulation
of the blood in the mesentery of a frog; but as the cruelty attendant on
these kinds of investigations would deprive the humane reader of a great
part of the gratification which might otherwise result from them, he
will probably rest satisfied with the accounts of such experiments to be
met with in authors; especially as there is an abundant variety of
objects on which he may exercise his ingenuity without sacrificing the
nicer feelings of humanity.[44]
[44] Whatever right mankind may claim over the lives of every creature
that is placed in a subordinate rank of being to themselves, in
respect of food and self-defence, as well as for the improvement of
science, and their judicious and ingenious application to the various
purposes of use and ornament in human life, we certainly cannot, on
the principles of reason and justice, assert a privilege to gratify a
wanton curiosity, or the sports of an inordinate fancy, by the
exercise of an unnecessary cruelty over them. The immortal SHAKSPEARE,
in a passage which has often been quoted, says,
------- the poor beetle that we tread upon
In corporal sufferance finds a pang as great
As when a giant dies.
It may, however, be doubted whether this particular instance is
strictly conformable to fact; different animals certainly possess
different degrees of sensibility, and some are consequently more
susceptible of pain than others. It is a remarkable circumstance that
the Hippobosca equina, or Horse-fly, will live, run, nay even
copulate, after being deprived of its head; most flies will survive
that loss for some time, and the loss of a leg or two does not prevent
their appearing as lively and alert as if they had sustained no
injury. Many insects, on being caught, will freely and voluntarily
part with their limbs to escape; and it is well known that lobsters
shed their claws. Numbers of other instances might be adduced, but on
this subject it may be prudent not to enlarge.
Montaigne remarks, that there is a certain claim of kindness and
benevolence which every species of creatures has a right to, from us.
It is to be regretted, that this general maxim is not more attended to
in the affairs of education, and pressed home upon tender minds in its
full extent and latitude; the early delight which children discover in
tormenting different animals should by all possible means be
discouraged, as, by being unrestrained in such sports, they may at
least acquire a habit of confirmed inattention to every kind of
suffering but their own, if not progressively be led to the
perpetration of more atrocious acts of cruelty. The supreme court of
judicature at Athens thought an instance of this sort not below its
cognizance, and punished a boy for putting out the eyes of a poor bird
that had unhappily fallen into his hands; and the inimitable HOGARTH,
“the great painter of mankind,” has in his “Five Stages of Cruelty,”
admirably depicted the consequences which may result from an early
indulgence of a propensity towards cruelty.
In order to awaken as early as possible in the minds of children an
extensive sense of humanity, it might be prudent to indulge them with
a view of several sorts of insects as magnified by the microscope, and
to explain to them that the same marks of divine wisdom prevail in the
formation of the minutest insect, as in the most enormous leviathan;
that they are equally furnished with whatever is necessary, not only
for the preservation, but the happiness of their beings, in that class
of existence which Providence has assigned them: in a word, that the
whole construction of their respective organs distinctly and
decisively, proclaims them the objects of divine benevolence, and
therefore they justly ought to be so of ours. EDIT.
OF ANIMALCULA IN INFUSIONS, &C.
These require little or no preparation. The first object is to procure
them, the second, to render them visible by the microscope. A few
observations, however, may be of use. Many drops of water may be
examined before any can be found; so that if the observer be too hasty,
he may be easily disappointed, though other parts of the same water may
be fully peopled by them.
The surface of infused liquors is generally covered with a thin
pellicle, which is easily broken, but acquires thickness by standing;
the greatest number of animalcula are generally to be found in this
superficial film.
In some cases it is necessary to dilute the infusions; but this is
always to be done with distilled water, and that water should be
examined in the microscope before it is made use of: the neglect of this
precaution has been a source of many errors.
Animalcula are in general better observed when the water is a little
evaporated, as the eye is not confused, nor the attention diverted by a
few objects. To separate one or two animalcula from the rest, place a
small drop of water on the glass near that of the infusion; make a small
neck or gutter between the two drops with a pin, which will join them
together; then the instant you perceive that an animalculum has
traversed the neck or gutter, and entered the drop, cut off the
communication between the two drops.
To procure the eels in paste, boil a little flower and water, till it
becomes of a moderate consistence; expose it to the air in an open
vessel, and beat it together from time to time, to prevent the surface
thereof from growing hard or mouldy; after a few days, especially in
summer time, it will turn sower, then if it be examined with attention,
you will find myriads of eels on the surface.
To preserve these eels all the year, you must keep the surface of the
paste moist, by putting a little water or fresh paste from time to time
to the other. Mr. Baker advises a drop or two of vinegar to be put into
the paste now and then. The continual motion of the eels, while the
surface is moist, will prevent the paste getting mouldy. Apply them to
the microscope upon a slip of flat glass, first putting on it a drop of
water, taken up by the head of a pin, for them to swim in.
To make an infusion of pepper. Bruise as much common black pepper as
will cover the bottom of an open jar, and lay it thereon about half an
inch thick; pour as much soft water in the vessel as will rise about an
inch above the pepper. The pepper and water are then to be well shaken
together; after which they must not be stirred, but be left exposed to
the air for a few days, when a thin pellicle will be formed on the
surface of the water, containing millions of animalcula.
The observer should be careful not to form a judgment of the nature, the
use, and the operations of small animalcula, from ideas which he has
acquired by considering the properties of larger animals: for, by the
assistance of glasses, we are introduced as it were into a new world,
and become acquainted not only with a few unknown animals, but with
numerous species thereof, which are so singular in their formation and
habits, that without the clearest proofs even their existence would not
be credited; and while they afford fresh instances of the Creator’s
power, they also give further proofs of the limits and weakness of the
human understanding.
DIRECTIONS FOR FINDING, FEEDING, AND PRESERVING THE POLYPES.
These little animals are to be found upon all sorts of aquatic plants,
upon branches of trees, pieces of board, rotten leaves, stones, and
other substances that lie in the water; they are also to be met with
upon the bodies of several aquatic animals, as on the water-snail, on
several species of the monoculus, &c. they generally fix themselves to
these by their tail, so that it is a very good method when you are in
search of the polypes, to take up a great many of these substances, and
put them in a glass full of water. If there be any polypes adhering to
these, you will soon perceive them stretching out their arms, especially
if the glass be suffered to be at rest for a while; for the polypes,
which contract themselves on being first taken out of the water, will
soon extend again when they are at rest.
They are to be sought for in the corners of ditches, puddles, and ponds,
being frequently driven into these with the pieces of wood or leaves to
which they have attached themselves. You may, therefore, search for them
in vain at one period, in a place where at another they will be found in
abundance. They are more easily perceived in a ditch when the sun shines
on the bottom, than at another time. In winter they are seldom to be met
with; about the month of May they begin to appear and increase.
They are generally to be found in waters which move gently; for neither
a rapid stream, nor stagnant waters ever abound with them. As they are
always fixed to some substance by their tails, and are very rarely loose
in the water, taking up water only can signify but little; a
circumstance which has probably been the cause of much disappointment to
those who have searched for them.
The green polypes are usually about half an inch long when stretched
out; those of the second and third sort are between three quarters of an
inch and an inch in length, though some are to be found at times which
are an inch and a half long.
Heat and cold has the same effect upon these little creatures, that it
has upon those of a larger size. They are animated and enlivened by
heat, whereas cold renders them faint and languid; they should therefore
be kept in such a degree of heat, that the water may not be below
temperate.
It is convenient for many experiments to suspend a polype from the
surface of the water. To effect this, take a hair pencil in one hand,
and hold a pointed quill in the other; with the pencil loosen the polype
from the receiver in which it is kept, and gradually raise it near the
top of the water, so that the anterior end may be next the point of the
pencil; then lift it out of the water, and keep it so for a minute;
after which, thrust the point of the pencil, together with the anterior
end, by little and little under water, until no more than about the
twentieth part of an inch of the polype’s tail remains above its
surface; at this instant, with the pointed quill remove that part of the
polype from the pencil which is already in the water, at the same time
blowing against the polype, by which it will be loosened, and remain out
of the water.
When the polypes were first discovered, Mr. Trembley had some difficulty
to find out the food which was proper for them; but he soon discovered,
that a small species of the millepede answered the purpose very well:
the pulices aquatices have also been recommended. The small red worms,
which are to be found on the mud-banks of the Thames, particularly near
the shores, answer the purpose also, they are easily found when the tide
is out, when they rise in such swarms on the surface of the mud, that it
appears of a red colour. These worms are an excellent food for the
polype. If a sufficient quantity be gathered in November, and put into a
large glass full of water, with three or four inches of earth at the
bottom, you will have a supply for the polypes all the winter. They may
also be fed with common worms, with the larva of gnats and other
insects, and even with butcher’s meat, &c. if it be cut small enough.
River, or any soft water, agrees with them; but that which is hard and
sharp prevents their thriving, and generally kills them in a few days.
The worms with which they are fed should be always cleansed before you
feed the polypes with them.
The polypes are commonly infested with little lice; from these it is
necessary to free them, in order to preserve your polypes in a good
state of health. They may be cleansed from the lice by rubbing them with
a hair pencil; this cannot be easily done, unless they adhere to some
substance: so that if they are suspended from the surface of the water,
you must endeavour to get them to fix themselves to a piece of
packthread; when they are fastened thereto, you may then rub them with a
hair pencil, without loosening them from the thread.
The lice which torment the polype are not only very numerous, but they
are also very large proportionably to its size: they may be said to be
nearly as large with respect to them, as a common beetle is to us. If
not rubbed off, they soon cover their bodies, and in a little time
totally destroy them.
To preserve the polypes in health, it is also necessary often to change
the water they are kept in, and particularly after they have done
eating; it is not sufficient to pour the water off, all the polypes
should be taken out, and the bottom and sides of the vessel rubbed from
the slimy sediment adhering thereto; this is caused by their fæces, and
is fatal to them if not cleaned away. The fæces often occasion a species
of mortification, which daily increases; its progress may be stopped by
cutting off the diseased part. To take them out, first loosen their
tails from the sides or bottom of the glass; then take them up one by
one, with a quill cut in the shape of a scoop, and place them in another
glass with clean water; if they cling to the quill, let it remain a
minute or two in the water, and they will soon disengage themselves.
They are preserved best in large glasses that hold three or four quarts
of water; for in a glass of this size the water need not be renewed so
often, particularly, if the fæces are taken out from time to time with
the feathered end of a pen, to which they readily adhere; and further,
the trouble of feeding each individual is in some measure saved, as you
need only throw in a parcel of worms, and let the polypes divide them
for themselves.
To observe with accuracy the various habitudes, positions, &c. of this
little animal, it will be necessary to place some of them in narrow
cylindrical glasses; then, by means of the microscope, Fig. 3. Plate VI.
you may observe them exerting all their actions of life with ease and
convenience; the facility with which the lens of the fore-mentioned
microscope may be moved and placed in any direction, renders it a most
convenient instrument for examining any object that requires to be
viewed in water.
It is also very proper to dry some of them, and place them between talcs
in a slider; this, however requires some dexterity and a little
practice; though, when executed with success, it fully rewards the pains
of the observer. Choose a proper polype, and put it into a small concave
lens, with a drop of water; when it is extended, and the tail fixed,
pour off a little of the water, and then plunge it with the concave into
some spirit of wine contained in the bowl of a large spoon; by this it
is instantly killed, the arms and body contracting more or less; rub it
gently while in the spirit with a small hair pencil, to cleanse it from
the lice.
The difficulty now begins; for the parts of the polype, on being taken
out of the spirit, immediately cling together, so that it is not
practicable to extend the body, and separate the arms on the talc,
without tearing them to pieces; therefore the only method is, to adjust
them upon the talc while in the spirit: this may be done by slipping the
talc under the body of the polype, while it lies in the spirit, and
displaying its arms thereon by the small hair pencil and a pair of
nippers; then lift the talc, with the polype upon it, out of the spirit;
take hold of it with the nippers in the left hand, dip the pencil in the
spirit with the right hand, and therewith dispose of the several parts,
that they may lie in a convenient manner, at the same time brushing away
any lice that may be seen upon the talc; now let it dry, which it does
in a little time, and place the talc carefully in the hole of the
slider. To prevent the upper talc and ring pressing on the polype, you
must cut three pieces of cork, about the bigness of a pin’s head, and
the depth of the polype, and fix them by gum in a triangular position,
partly on the edges of the said talc, and partly to the sides of the
ivory hole itself; the upper talc may then be laid on these corks, and
pressed down by the ring as usual.[45]
[45] Baker on the Polypes.
OF VEGETABLES.
It were to be wished a satisfactory account could here be given of all
the preparations which are requisite to fit for the microscope the
objects of the vegetable kingdom. Dr. Hill is the only writer who has
handled this subject. I shall, therefore, extract from his “Treatise on
the Construction of Timber,” what he has said; this, together with the
improvements I have made on the cutting engine, will enable the reader
to pursue the subject and extend it further, both for his own pleasure,
and the advantage of the public.
THE MANNER OF OBTAINING THE PARTS OF A SHOOT SEPARATE.
In the beginning of April, take a quantity of young branches from the
scarlet oak, and other trees. These are first cut into lengths, of the
growth of different seasons; and then part is left entire, part split,
and the rest quartered. In this state they are put into a wicker basket,
with large openings, or of loose work, and a heavy stone is put in with
them; a rope is tied to the handle of the basket, and it is thrown into
a brook of running water: at times it is taken up, and exposed a little
to the air; it is frequently shook about under water, to wash off filth;
and once in ten days the sticks are examined.
By degrees the parts loosen from one another, and by gentle rubbing in a
bason of water just warmed, they will be so far separated, that a pencil
brush will perfect the business, and afford pieces of various sizes,
pure, distinct, and clean. One part will in this way separate at one
time, and another, at another; but by turning the sticks to the water,
and repeating the operation, in the course of four or five weeks every
part may be obtained distinct. They are best examined immediately; but
if any one wish to preserve them for repeated inquiries, it may be done
in this manner: dissolve half an ounce of alum in two quarts of water;
drop the pieces thus separated, for a few moments, into this solution,
then dry them upon paper, and put them up in vials of spirit of wine, no
other fluid being so well adapted to preserve these tender bodies.
TO PREPARE THE RIND FOR OBSERVATION.
As the vessels of the rind are of different diameters in various trees,
though their construction and that of the blebs is perfectly the same in
all, it will be best to choose for this purpose the rind of a tree
wherein they are largest. The rind of the ash-leaved maple is finely
suited. A piece of this may be obtained of two inches long, and will
very successfully answer the intention. Such a piece being prepared
without alum or spirit, but dried from the water in which it had been
macerated, it is to be impregnated with lead in the following manner, to
shew the apertures by their colour.
Dissolve one drachm of sugar of lead in an ounce and an half of water;
filter this through paper, and pour it into a tea-cup. Clip off a thin
slice of what was the lower end of the piece of rind as it grew on the
tree, and plunge it near an inch deep into the liquor; keep it upright
between two pieces of stick, so that one half or more may be above the
water; whelm a wine-and-water glass over the tea-cup, and set the whole
in a warm place. When it has stood two days, take it out, clip off all
that part which was in the liquor, and throw it away.
The circumstances here mentioned, trivial as they may seem, must be
attended to: the operation will not succeed, even if the covering-glass
be omitted; it keeps a moist atmosphere about the rind, and makes its
vessels supple.
While this is standing, put into a bason two ounces of quick lime, and
an ounce of orpiment; pour upon them a pint and an half of boiling
water; stir the whole together, and when it has stood a day and a night,
it will be fit for use. This is the “liquor probatorius vini” of some
of the German chymists; it discovers lead when wines are adulterated
with it, and will shew it any where.
Put a little of this liquor in a tea-cup, and plunge the piece of rind
half way into it.
In the former part of this experiment, the vessels of the rind have been
filled with a solution of lead, that makes of itself no visible
alteration in them; but this colourless impregnation, when the orpiment
lixivium gets to it, becomes of a deep brown; the vessels themselves
appear somewhat the darker for it; but these dots, which are real
openings, are now plainly seen to be such, the colour being perfectly
visible in them, and much darker than in the vessels. This object must
be always viewed dry.
If a piece of the rind, thus impregnated, be gently rubbed between the
fingers, till the parts are separated, we shall be able in one place or
other, to get a view of the vessels all round, and of the films which
form the blebs between them.
Every part of the rind, and every coat of it, even the interstitial
place between its innermost coat and bark, are filled with a fine fluid.
The very course and progress of the fluid may be shewn in this part,
even by an easy preparation; only that different rinds must be sought
for this purpose, the vessels in some being larger than in others.
Repeated trials have shewn me that the whole progress may be easily
marked in the three following kinds, with only a tincture of cochineal.