ling tulips, become
larger and stronger in the second year than the first, and thus
improve till they acquire flowers or sexes; and the aphis, I believe,
increases in bulk to the eighth or ninth generation, and then produces
a sexual progeny. Hence the existence of spontaneous vitality is only
to be expected to be found in the simplest modes of animation, as the
complex ones have been formed by many successive reproductions.

_Experimental facts._

III. By the experiments of Buffon, Reaumur, Ellis, Ingenhouz, and
others, microscopic animals are produced in three or four days,
according to the warmth of the season, in the infusions of all
vegetable or animal matter. One or more of these gentlemen put some
boiling veal broth into a phial previously heated in the fire, and
sealing it up hermetically or with melted wax, observed it to be
replete with animalcules in three or four days.

These microscopic animals are believed to possess a power of
generating others like themselves by solitary reproduction without
sex; and these gradually enlarging and improving for innumerable
successive generations. Mr. Ellis in Phil. Transact. V. LIX. gives
drawings of six kinds of animalcula infusoria, which increase by
dividing across the middle into two distinct animals. Thus in paste
composed of flour and water, which has been suffered to become
acescent, the animalcules called eels, vibrio anguillula, are seen in
great abundance; their motions are rapid and strong; they are
viviparous, and produce at intervals a numerous progeny: animals
similar to these are also found in vinegar; Naturalist's Miscellany by
Shaw and Nodder, Vol. II. These eels were probably at first as minute
as other microscopic animalcules; but by frequent, perhaps hourly
reproduction, have gradually become the large animals above described,
possessing wonderful strength and activity.

To suppose the eggs of the former microscopic animals to float in the
atmosphere, and pass through the sealed glass phial, is so contrary to
apparent nature, as to be totally incredible! and as the latter are
viviparous, it is equally absurd to suppose, that their parents float
universally in the atmosphere to lay their young in paste or vinegar!

Not only microscopic animals appear to be produced by a spontaneous
vital process, and then quickly improve by solitary generation like
the buds of trees, or like the polypus and aphis, but there is one
vegetable body, which appears t