fometimes obliquely, fometimes ftrait forwards, at other times
circularly, one while rolling and turning round, and then running
backwards and forwards through the whole dimenfions of the
drop, as if in fport; at other times attacking with avidity the
little heaps of matter they meet with in their way. They know
how to avoid with dexterity any obftacles that would interrupt
their motion, and even to avoid one another ; you may fee hundreds
in motion in a drop o f water, that never ftrike againft each
other; fometimes they will fuddenly change the direriion in
which they are moving, and take one diametrically oppofite
thereto. By inclining the glafs on which the drop of water is
laid, it may be made to move in any direction ; the animalcula
in the drop will fwim as eafily againft the ftream as with it.
I f the water begins to evaporate, and the drop to grow fmaller,
they flock impetuoufly towards the remaining fluid ; an anxious
delire of attaining this momentary refpite o f life is very vifible, as
well as an uncommon agitation of the organs by which they imbibe
the water. Thefe motions grow languid as the water fails,
till they at laft ceafe. I f they are left dry for a little time, it is im-
poflible to re-animate them by giving them frelh water.
Animalcula and infefts will fupport a great degree o f cold, but
both one and the other perilh when it is carried beyond a certain
point. The fame degree o f heat that deftroys the exiftence of
infefls, is fatal to animalcula ; as there are animalcula produced
in water at the freezing point, fo there are infefls which live in
fnow.
I f
I f the fmalleft drop o f urine is put into a drop o f water, where
thefe animalcula are roving about, apparently happy and eafy
they inftantly fly to the other fide, but the acid foon communicating
itfelf to this part, their ftruggles to efcape are increafed,
but the evil alfo increafing, they are thrown into convulfions, and
foon expire.
Among animalcula, as in every other part o f nature, there is
always a certain proportion preferved between the fize of the individuals
and their number. There are always feweft amongft the
larger kinds, but they increafe in number as they diminilh in fize,
till o f the laft or loweft to which our powers o f magnifying will
reach, there are myriads to one o f the larger. Like other animals,
they increafe in fize from their birth till they have attained
their full growth. When deprived o f food, they grow thin and
perilh, and different degrees o f organization are to be difcovered
in their ftru&ure.
The birth and propagation o f thefe mierofcopic beings is as
regular as that of the largeft animals o f our globe; for though
them extreme mmutenefs prevents us, in moll cafes,, from feeing
the germ from which they fpring, yet we are well allured, from
numerous obfervations, that the manner in which they multiply is
regulated by conftant and invariable laws. .
We have Teen that different Aperies o f the hydra and vorticella
multiply and increafe by natural divifions and fubdivifions o f the
parent s body \ this manner o f propagation is very common among
the animalcula in infufions, though with many remarkable varieties.
Some multiply by a tranfverfe divifion, a contraction
3 & 2 takes