in number, living in a kind of slimy mucilaginous case, which, when
expanded in the water, has some resemblance to a bell with its mouth
upwards. These bells or colonies are to be found adhering to the large
leaves of duck-weed and other aquatic plants.
The bell or case which these animals inhabit, being very transparent,
all the motions of its inhabitants may be discerned distinctly through
it. There are several ramifications or smaller bells proceeding from the
larger one; in each of these there is an inhabitant. The opening at the
top of these bells is just large enough for the creature’s head, and a
small part of its body to be thrust out from it, the rest remaining in
the case, into which it also draws the head on the least alarm.
Besides the particular and separate motions which each of these
creatures is able to exert within its case, and independent of the rest,
the whole colony has a power of altering the position of the bell, and
removing it from one place to another. These animalcula seem not to like
to dwell in societies, whose number exceeds fifteen; when the colony
happens to increase in number, the bell may be observed to split
gradually, beginning from about the middle of the upper extremity, and
proceeding downwards towards the bottom, till they at last separate and
become two colonies, independent of each other.
The arms are very near each other; sixty may often be counted in one
plume, having each the figure of an Italic _ʃ_, one of whose hooked ends
is fastened to the head; and altogether, when expanded, compose a figure
somewhat like a horseshoe, convex on the side next the body, but
gradually opening and turning outwards, so as to leave a considerable
distance within the outer extremities of the arms.
The plumed polype is of a very voracious disposition, devouring a great
number of small animals. If the arms, when extended, be observed
attentively with the microscope, they will be found to have a constant
vibratory motion; alternately bending withinside of the plume, and then
rising up again. When one arm ceases its motion, the same is performed
by another; thus by the perpetual agitation of the several arms, such a
strong current is produced in the water, as brings the animalcula, and
other minute bodies, that are floating near the polype, into its mouth,
which is situated between the arms. The food, if agreeable to the
creature, is swallowed; if otherwise, it is rejected by a contrary
motion.
The animal may be seen very plain when it has retired within the tube.
The body is about one-eighth of an inch long, without reckoning the
plume, which is about the same length. It is cylindrical, and the skin
is very transparent. The plume is only a continuation of this
transparent skin, it is very broad in proportion to the body, and of a
remarkable figure; the base is of the shape of a horseshoe; from this
base the arms project, they bend rather outwards. The plume which they
form, gives them a resemblance to some flowers. The arms may be
compared, from their fineness and transparency, to very fine threads of
glass. The base of the plume is grooved, and is fixed to the animal by
the middle of the horseshoe which it forms, and it is here that there is
an opening which serves as a mouth to the animal. The intestines are
easily distinguished through its transparent skin; when it has just been
eating, they are of a deep brown colour. Three principal parts are very
visible, the oesophagus, the stomach, and the rectum.
In the inside of these animals a small oblong whitish body is formed,
which is carried to the outside, and remains fixed in a perpendicular
direction to the body; many of these are formed daily, and of these
oval bodies new animals are produced, exactly similar to the parent.
If these minute bodies be eggs, they are of a singular kind, being
destitute of any covering, and are neither membranaceous nor
crustaceous; we cannot with propriety say the young ones are hatched
from them; we can, however, perceive these oviform bodies to unfold
themselves gradually. The developement is accomplished in a few minutes,
and an animalculum appears like the parent.
Trembley amassed a great number of these eggs, and carried them from
England with him, keeping them quite dry; on putting them into water,
they gradually developed, and became as perfect as the tubularia from
which they proceeded.
There is a very great similarity in the construction of this little
creature and many of the marine polypes, who, like it, exist in tubes of
the same growth with themselves.
Fig. 32 represents three tubulariæ campanulatæ or plumed polypes very
much magnified, namely, one, b f a c d d e h g i, which is out of its
cell; e h, the oesophagus; f g, the stomach; a f, the rectum; a c d d e,
the plume, consisting of the base a e, which is but little seen, and the
arms c d d, which proceed from the edges of this base; a second polype,
_A B I_, which is within its cell, and in which the skin containing the
plume is reversed. The third polype, s t u u, is a young one exhibited
out of its cell; g o o, threads which are fixed at one end to the
intestines of the animal, by the other to the bottom of the cell, l k.
CHAP. VIII.
OF THE ANIMALCULA INFUSORIA.
Our knowledge of the microscopic world is at present very contracted,
but we know enough to give us high conceptions of its concealed wonders,
and to fill us with profound astonishment at the infinite variety of
forms that are made recipient of life. A few of the inhabitants of this
minute world have been discovered. The figure and apparent habits of
life of these, resemble so little those with which we are more
acquainted, that it is often difficult to find terms to express what is
represented to the eye.
Animalculum signifies a little animal, and therefore the term might be
applied to every animal which is considerably inferior in size to
ourselves. It has been customary, however, to distinguish by the name of
animalcula only such animals as are of a size so diminutive, that their
true figure cannot be discerned without the assistance of glasses; and
more especially it is applied to such as are altogether invisible to the
naked eye, and cannot even be perceived to exist, but by the aid of
microscopes.
By the help of magnifying glasses we are brought into a kind of new
world; and numberless animals are discovered, which, from their
minuteness, must otherwise for ever have escaped our observation: and
how many kinds of these invisibles there may be, is yet unknown; as they
are observed of all sizes, from those which are barely invisible to the
naked eye, to such as resist the action of the microscope, as the fixed
stars do that of the telescope, and with the best magnifiers hitherto
invented, appear only as so many moving points.
The smallest living creatures our instruments can shew, are those that
inhabit the waters; for, though possibly animalcula equally minute, or
perhaps more so, may fly in the air, or creep upon the earth, it is
scarce possible to obtain a view of them; whereas, water being
transparent, and confining the creatures within it, we are enabled, by
applying a drop of it to our glasses, to discover with ease a great part
of its contents, and in a space barely visible to the naked eye, often
perceive a thousand little creatures, all full of life and vigour.
By the animalcula infusoria are meant, not the larvæ of those insects
which in their first state are inhabitants of water, and afterwards
become winged insects, as the gnat, &c. Baker, and many other writers on
the subject, have often confounded these, and hence entered into a train
of reasoning contrary to fact and experience. The animalcula infusoria
take their name from their being found in all kinds either of vegetable
or animal infusions; if seeds, herbs, or other vegetable substances, be
infused in water, it will soon be filled with an indefinite number of
these minute beings. There is a prodigious variety in their forms; some
perfectly resemble the bell-polype; others are round or oblong, without
any, at least apparent, members; some resemble a bulb with a long taper
tail; some are nearly spherical; the greater part are vesicular and
transparent. Those most generally found in every drop of ditch water are
mere inflated bladders, with a small trace of intestines in the center;
the next are a flat kind, with a number of legs under the belly.
Motion seems to be their great delight; they pervade with equal ease and
rapidity, and in all forms and directions, the whole dimensions of the
drop, in which they find ample space for their various progressions,
sometimes darting straight forward, at other times moving obliquely,
then again circularly: they know how to avoid with dexterity any
obstacles that might obstruct their progress. Hundreds may be seen in a
drop of water in constant action, yet never striking against each other.
If at any time the clusters prove so thick as to impede any of their
motions, they roll and tumble themselves over head, creep under the
whole range, force their way through the midst, or wheel round the
cluster, with surprizing swiftness; sometimes they will suddenly change
the direction in which they are moving, and take one diametrically
opposite thereto. By inclining the glass on which the drop of water is
laid, it may be made to move in any direction; the animalcula in the
drop will swim as easily against the stream as with it.
If the water begin to evaporate, and the drop to grow smaller, they
flock impetuously towards the remaining part of the fluid; an anxious
desire of attaining this momentary respite of life is very visible, as
well as an uncommon agitation of the organs by which they imbibe the
water. These motions grow more languid as the water fails, till at last
they entirely cease.
Animalcula and insects will support a great degree of cold, but both one
and the other perish when it is carried beyond a certain point. The same
degree of heat that destroys the existence of insects, is fatal to
animalcula; as there are animalcula produced in water at the freezing
point, so there are insects which live in snow.
If the smallest drop of urine be put into a drop of water where these
animalcula are roving about, apparently happy and easy, they instantly
fly to the other side, but the acid soon communicating itself to this
part, their struggles to escape are increased, but the evil also
increasing, they are thrown into convulsions, and soon expire.
Among animalcula, as in every other part of nature, there is constantly
a certain proportion preserved between the size of the individuals and
their number. There are always fewest amongst the larger kinds, but they
increase in number as they diminish in size, till of the last, or lowest
to which our powers of magnifying will reach, there are myriads to one
of the larger. Like other animals, they increase in size from their
birth till they have attained their full growth. When deprived of food,
they grow thin and perish; and different degrees of organization are to
be discovered in their structure.
The birth and propagation of these microscopic beings is as regular as
that of the largest animals of our globe; for though their extreme
minuteness prevents us, in most cases, from seeing the germ from which
they spring, yet we are well assured, from numerous observations, that
the manner in which they multiply is regulated by constant and
invariable laws.
It has been shewn that different species of the hydræ and vorticellæ
multiply and increase by natural divisions and subdivisions of the
parent’s body; this manner of propagation is very common among the
animalcula in infusions, though with many remarkable varieties. Some
multiply by a transverse division, a contraction takes place in the
middle, forming a kind of neck that becomes smaller every instant, till
they are enabled by a slight degree of motion to separate from each
other. These animalcula in general studiously avoid each other; but when
they are in the labour of multiplication, and the division is in great
forwardness, it is not uncommon to see one of them precipitate itself on
the neck of the dividing animalculum, and thus accelerate the
separation.
Another species, when it is on the point of multiplying, fixes itself to
the bottom of the infusion; it then forms an oblong figure, afterwards
becomes round, and begins to turn rapidly, as if upon an internal
center, continually changing the direction of its rotatory motion; after
some time, we may perceive two lines on the spherule, forming a kind of
cross; soon after which the animalculum divides into four distinct
beings, which grow, and are again subdivided.
Some multiply by a longitudinal division, which in one kind begins in
the fore-part, and others in the hind-part; from another kind a small
fragment is seen to detach itself, which very soon acquires the form of
the parent animalculum. Lastly, some propagate in the same manner as
those we deem more perfect animals.
From what has been said, it appears clearly that their motions are not
purely mechanical, but are produced by an internal spontaneous
principle, and that they must therefore be placed among the class of
living animals, for they possess the strongest marks, and the most
decided characters of animation; and consequently, that there is no
foundation for the supposition of a chaotic and neutral kingdom, which
can only have derived its origin from a very transient and superficial
view of these animalcula.
It may also be further observed, that as we see the motions of the
limbs, &c. of the more noble animals, viz. the human species, are
produced by the mechanical construction of the body and the action of
the soul thereon, and are forced by the ocular demonstration arising
from anatomical dissection, to acknowledge this mechanism which is
adapted to produce the various motions necessary to the animal; and as
when we have recourse to the microscope, we find those pieces which had
appeared to the naked eye as the primary mechanical causes of the
particular motions, to consist themselves of lesser parts, which are the
causes of motion, extension, &c. in the larger; when the structure can
therefore be traced no further by the eye or glasses, we have no right
to conclude, that the parts which are invisible, are not equally the
subject of mechanism: for this would be only to assert in other words,
that a thing may exist because we see and feel it, and has no existence
when it is not the object of our senses.
The same train of reasoning may be applied to microscopic insects and
animalcula; we see them move, but because the muscles and members which
occasion these motions are invisible, shall we infer that they have not
muscles, with organs appropriated to the motion of the whole and its
parts? To say that they exist not, because we cannot perceive them,
would surely not be a rational conclusion. Our senses are indeed given
us, that we may comprehend some effects; but then we have also a mind
with reason bestowed upon us, that from the things which we do perceive
with our senses, we may deduce the nature of those causes and effects
which are imperceptible to the corporeal eye.
Messrs. Buffon, Needham, and Baron Münchhausen, have considered this
part of animated nature in so different a light from other writers, that
we cannot with propriety entirely pass them over. Needham imagined that
there was a vegetative force in every microscopical point of water, and
every visible filament of which the whole vegetable contexture consists;
that the several species of microscopic animals may subside, resolve
again into gelatinous filaments, and again give lesser animals, and so
on, till they can be no further pursued by glasses. That agreeable to
this idea, every animal or vegetable substance advances as fast as it
can in its revolution, to return by a slow descent to one common
principle, whence its atoms may return again, and ascend to a new life.
That notwithstanding this, the specific seed of one animal can never
give another of a different species, on account of the preparation it
must receive to constitute it this specific seed.
Buffon asserts, that what have been called spermatic animals, are not
creatures really possessing life, but something proper to compose a
living creature, distinguishing them by the name of organic particles,
and that the moving bodies which are to be found in the infusions either
of animal or vegetable substances, are of the same nature.
Baron Münchhausen supposed that the seeds of mushrooms were first
animals, and then vegetables; and this, because he had observed some of
the globules in the infusions of mushrooms, after moving some time, to
begin to vegetate.
It might be sufficient in the first instance to observe, that Messrs.
Needham, and Buffon, by having recourse to a vegetative force and
organic particles, to account for the existence and explain the nature
of animalcula, and the difficulties of generation, have substituted
words in the place of things; and that we are no gainers by the
substitution, unless they explain the nature of these powers. But to
this we may add, that all those who have examined the subject with
accuracy and attention, as Bonnet, De Saussure, Baker, Wrisberg,
Spalanzani, Haller, Ellis, Müller, Ledermüller, Corti, Rofredi, &c.
disagree with the foregoing gentlemen, proving that they had deceived
themselves by inaccurate experiments, and that one of them, Buffon, had
not seen the spermatic animals he supposed himself to be describing,
insomuch that Needham was at last induced to give up his favourite
hypothesis.
Though we can by no means pretend to account for the appearance of most
animalcula, yet we cannot help observing, that our ignorance of the
cause of any phænomenon is no argument against its existence. Though we
are not, for instance, able to account in a satisfactory manner for the
origin of the native Americans, yet we suppose Buffon himself would
reckon it absurd to maintain, that the Spaniards on their arrival there
found only ORGANIC PARTICLES moving about in disorder. The case is the
very same with the eels in paste, to whose animation he objects. They
are exceedingly small in comparison with us; but, with the solar
microscope, Baker has made them assume a more respectable appearance, so
as to have a diameter of an inch and an half, and a proportionable
length. They swam up and down very briskly; the motion of their
intestines was very visible; when the water dried up they died with
apparent agonies, and their mouths opened very wide. Now, were we to
find a creature of the size of this magnified eel gasping in a place
where water had lately been, we certainly should never conclude it to be
merely an ORGANIC PARTICLE, or fortuitous assemblage of them, but a
fish. Why then should we conclude otherwise with regard to the eel in
its natural state, than that it is a little fish? In reasoning on this
subject, we ought ever to remember, that however essential the
distinction of bodies into great and small may appear to us, they are
not so to the Deity, with whom, as Baker well expresses himself, “an
atom is a world, and a world but as an atom.” Were the Deity to exert
his power a little, and give a natural philosopher a view of a quantity
of paste filled with eels, from each of whose bodies the light was
reflected as in the solar microscope; our philosopher, instead of
imagining them to be mere organic particles, as the paste would appear
like a little mountain, he would probably look upon the whole as an
assemblage of serpents, and be afraid to come near them. Whenever,
therefore, we discover beings to appearance endued with a principle of
self-preservation, or whatever we make the characteristic of animals,
neither the smallness of their size, nor the impossibility of our
knowing how they came there, ought to cause us to doubt of their being
animated.
I shall here insert some extracts of the experiments made by Ellis at
the desire of Linnæus, and which are a full refutation of those made by
Needham and Münchhausen. By those he made on the infusions of mushrooms
in water, it appeared evidently that the seeds were put in motion by
minute animals, which arose on the decomposition of the mushroom; these,
by pecking at the seeds, which are little round reddish bodies, moved
them about with great agility in a variety of directions, while the
little animals themselves were scarce visible till the food they had
eaten discovered them.
The ramified filaments, and jointed or coralloid bodies, which the
microscope discovers to us on the surface of most vegetable and animal
infusions, when they become putrid, and which were supposed by Needham
to be zoophytes, were found by Ellis to be of that genus of fungi called
mucor, many of which have been figured by Michelius, and described by
Linnæus. Their vegetation is so quick, that they may be seen to grow and
seed under the eye of the observer. Other instances of similar mistakes
in Needham’s experiments may be seen in Ellis’s paper, Philos. Trans.
vol. lix. p. 138.
A species of mucor arises also from the bodies of insects putrefying in
water; this species sends forth a mass of transparent filamentous roots,
from whence arise hollow seed vessels; on the top there is a hole, from
which minute globules often issue in abundance, and with considerable
elastic force, which move about in the water. It will however be found,
with a little attention, that the water is full of very minute
animalcula, which attack these seeds, and thus prolong their motion; but
after a small space of time they rise to the surface, and remain there
without any motion; a fresh quantity rises up, and floating to the edge
of the water, remains there inactive; but no appearance can be observed
of detached and separated parts becoming what are called microscopic
animalcula. Indeed, it is surprizing that Needham should ever take the
filaments of the moistened grains for any thing else than a vegetable
production, a true species of mouldiness.
On the 25th of May, Fahrenheit’s thermometer 70°, Ellis boiled a potatoe
in the New River water, till it was reduced to a mealy consistence. He
put part of it, with an equal proportion of the boiling liquor, into a
cylindrical glass vessel, that held something less than half a wine
pint, and covered it close immediately with a glass cover. At the same
time he sliced an unboiled potatoe, and, as near as he could judge, put
the same quantity into a glass vessel of the same kind, with the same
proportion of New River water not boiled, and covering it with a glass
cover, placed both vessels close to each other. On the 26th of May,
twenty-four hours afterwards, he examined a small drop of each by the
first magnifier of Wilson’s microscope, whose focal distance is reckoned
at ¹⁄₅₀ part of an inch; and, to his amazement, they were both full of
animalcula of a linear shape, very distinguishable, moving to and fro
with great celerity; so that there appeared to be more particles of
animal than vegetable life in each drop. This experiment he repeatedly
tried, and always found it to succeed in proportion to the heat of the
circumambient air; so that even in winter, if the liquors be kept
properly warm, at least in two or three days the experiment will
succeed.
The animalcula are infinitely smaller than spermatic animals, and of a
very different shape; the truth of which every accurate observer will
soon be convinced of, whose curiosity may lead him to compare them, and
he is persuaded they will find they are no way akin. Having learnt from
M. De Saussure, of Geneva, that he found one kind of these animalcula
infusoria that increases by dividing across into nearly two equal parts,
and that the infusion was made from hemp-seed, he procured a quantity of
this seed, some of it he put into New River water, some into distilled
water, and some into very hard pump water; the result was, that in
proportion to the heat of the weather, or the warmth in which they were
kept, there was an appearance of millions of minute animalcula in all
the infusions; and some time after some oval ones made their appearance;
these were much larger than the first, which still continued. These
wriggled to and fro in an undulatory motion, turning themselves round
very quick all the time that they moved forwards.