A theory that animalcules are the cause of the various contagious
and infectious disorders has created much discussion; and
although this opinion is not generally entertained by the
faculty, the idea is so feasible, and so many rational arguments
can be brought forward in its support, that I cannot help
touching upon a topic so generally interesting.
In the first place, nearly all infectious diseases predominate in
localities which are hot, damp, swampy, abounding in stagnant
pools and excluded from a free circulation of air. In a tropical
country, a residence in such a situation would be certain death
to a human being, but the same locality will be found to swarm
with insects and reptiles of all classes.
Thus, what is inimical to human life is propitious to the insect
tribe. This is the first step in favor of the argument.
Therefore, whatever shall tend to increase the insect life must
in an inverse ratio war with human existence.
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.
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