superior to us and to our ordinary animals as
we and our animals are to microscopic animalcules,
and who, moreover, observe us with
their microscopes frisking about our world, as
we observe the infinite multitude of animalcules
with ours. Bernoulli went further; he
asserted that animals incomparably larger
than those might exist; and he would have
as many degrees in the ascending scale as he
actually found in the descending scale of
magnitude; for he would not allow man and
his fellow-creatures to constitute the highest
degree. On the other hand, Leibnitz believed
that, here, the smallest grain of sand, the
minutest atom, may contain whole worlds
which are not inferior to ours in beauty and
variety. The great observer, Leuwenhoek,
was so completely carried away by his
admiration of the new creation revealed to him by
the microscope, that he imagined an infinity
of perfect organisation beyond the infinite
details displayed by his instruments in every
object of living nature. He enthusiastically
supposed that the incredibly slender tails of
certain so-called animalcules were composed
of tendons, muscles, and jointed bones, exactly
like the tail of a rat or a monkey; and, reasoning
thus from analogy, he attributed to these
minutest creatures a system of viscera as
complicated as that of the largest animals.
Ehrenberg, led on likewise by false analogy,
outstepped even Leuwenhoek in the marvel
lous riches of organisation with which he
endowed the Infusoria, giving them nervous
ganglia, stomachs, muscles, and entrails.

The latest discoveries compel us to reject
such ideas, on finding that they are not based
on facts. For, even supposing that it were a
law of nature that there is no limit to the
divisibility of matter—and a multitude of
physical and chemical phenomena tend to
prove the contrary—that law would not
suffice to prove the possibility of an extremely
complex organisation beyond a certain limit
of minuteness. It is well known that many
physical and dynamical phenomena are
considerably altered, or are even entirely
suppressed, when it is attempted to make them
occur in too confined a space, or on bodies of
too minute dimensions. For instance: liquid
ceases to flow, even under heavy pressure, in
a capillary tube, whose diameter is less than
a certain fixed measurement. That circumstance
puts a limit to the size of arteries and
veins. It is much more consonant, therefore,
with the laws of physics to allow that, in these
tiny animals, the fluids penetrate simply by
absorption, than to furnish them hypothetically
with a heart and a circulation, especially
as our best instruments do not give us the
least hint of their existence. Besides, we
do not find that the elementary parts of
which the larger animals are composed,
gradually decrease in size in proportion to the
smaller stature of the animals themselves.
On the contrary, the blood discs, the muscular
fibres, and the capillary vessels, are very much
of the same dimensions in the elephant as
they are in the mouse.

It is known that solid bodies, when reduced
to particles of extreme minuteness, cease in
some sort to be subject to the laws of weight
and inertia. There must, therefore, be a limit
somewhere to the magnitude of material
life. We may reasonably suppose that that
limit is attained by the smallest animalcule
shown by our microscopes; because at that
point of minuteness, or a little beyond it, the
properties acquired by such extremely small
molecules counterbalance the other physical
laws. Nature, therefore, instead of producing
a complex machinery which would not act
under existing circumstances, has adapted her
creatures to those circumstances. She has
placed her minutest progeny in a liquid
medium, to whose conditions they are fitted, so
as to render such complexity of organisation
unnecessary. She has created the marvellous
order of microscopic animals which live
in water, or on extremely damp substances,
and which, not wanting either true muscles,
vessels, or nerves, are not furnished with
them. Take a drop of water from the nearest
pool or ditch, especially that which is charged
with saline matters and organic substances
in a state of decomposition; submit it to
your microscope, and you will be sure to see
innumerable minute beings in active motion;
these are Infusoria, or the animalcules of
infusions. The name, though it has been
criticised, is apt and strictly true. For
wherever stagnant water contains decaying
animal or vegetable matter, it is a true infusion.
All such waters, whether salt or fresh,
are the grand rendezvous of the Infusories.

These minute creatures, so little thought of
by the world in general, have a complete
physiology, anatomy, and natural history of
their own, which are quite as interesting to
study as those of the larger animals—more
so, perhaps. Because although able and
voluminous works on the Infusoria exist,
their systematic arrangement has to be
remade from the beginning, and their personal
biography remains for the greater part a
mystery. Indeed, the curious forms and
vivacious actions exhibited by the majority
of Infusories are one great cause of the
absorbing attraction which the microscope
exercises on its votaries. It is scarcely
possible to quit them, however fatigued one's
eyes may be. After a last look, we yield to
the temptation of one look more. The
miraculous instrument began its career by killing
its foster-father, Swammerdam; and it has
robbed a host ot other devotees, if not of
their life, at least of their perfect vision.
They have become myopic—which should be
a warning to us—in consequence of gazing
too long and too intently at their microcosm.
But the seduction is irresistible; one glimpse
at truth and actual life sets us athirst for
more intimate views of nature. The craving
after knowledge is a passion which is never