fusion of
Potatoes and Hempseed; Philos. Transact. Vol. LIX. from all which it
would appear, that organic particles of dead vegetables and animals
during their usual chemical changes into putridity or acidity, do not
lose all their organization or vitality, but retain so much of it as
to unite with the parts of living animals in the process of nutrition,
or unite and produce new complicate animals by secretion as in
generation, or produce very simple microscopic animals or microscopic
vegetables, by their new combinations in warmth and moisture.

And finally, that these microscopic organic bodies are multiplied and
enlarged by solitary reproduction without sexual intercourse till they
acquire greater perfection or new properties. Lewenhoek observed in
rain-water which had stood a few days, the smallest scarcely visible
microscopic animalcules, and in a few more days he observed others
eight times as large; English Encyclop. Art. Animalcule.

_Conclusion._

There is therefore no absurdity in believing that the most simple
animals and vegetables may be produced by the congress of the parts of
decomposing organic matter, without what can properly be termed
generation, as the genus did not previously exist; which accounts for
the endless varieties, as well as for the immense numbers of
microscopic animals.

The green vegetable matter of Dr. Priestley, which is universally
produced in stagnant water, and the mucor, or mouldiness, which is
seen on the surface of all putrid vegetable and animal matter, have
probably no parents, but a spontaneous origin from the congress of the
decomposing organic particles, and afterwards propagate themselves.
Some other fungi, as those growing in close wine-vaults, or others
which arise from decaying trees, or rotten timber, may perhaps be
owing to a similar spontaneous production, and not previously exist as
perfect organic beings in the juices of the wood, as some have
supposed. In the same manner it would seem, that the common esculent
mushroom is produced from horse dung at any time and in any place, as
is the common practice of many gardeners; Kennedy on Gardening.

_Appendix._

The knowledge of microscopic animals is still in its infancy: those
already known are arranged by Mr. Muller into the following classes;
but it is probable, that many more classes, as well as innumerable
individuals, may be discovered by improvements of the microscope, as
Mr. Herschell has discovered