When we examine a drop of impure water, and discover by the
microscope the thousands of living beings which not only are
invisible to the naked eye, but some of whom are barely
discoverable even by the strongest magnifying power, it certainly
leads to the inference, that if one drop of impure fluid contains
countless atoms endowed with vitality, the same amount of impure
air may be equally tenanted with its myriads of invisible
inhabitants.
It is well known that different mixtures, which are at first pure
and apparently free from all insect life, will, in the course of
their fermentation and subsequent impurity, generate peculiar
species of animalcules. Thus all water and vegetable or animal
matter, in a state of stagnation and decay, gives birth to insect
life; likewise all substances of every denomination which are
subjected to putrid fermentation. Unclean sewers, filthy hovels,
unswept streets, unwashed clothes, are therefore breeders of
animalcules, many of which are perfectly visible without
microscopic aid.
Now, if some are discernible by the naked eye, and others are
detected in such varying sizes that some can only just be
distinguished by the most powerful lens, is it not rational to
conclude that the smallest discernible to human intelligence is
but the medium of a countless race? that millions of others still
exist, which are too minute for any observation?
