constitution, a supposed peculiar condition of the body due to changes
in the character of the air, or to the climate, or to changes in the
interior of the earth as shown by earthquakes, or to the movements of
planets; in consequence of this peculiar constitution there was a
greater susceptibility to disease, but the direct cause might arise in
the interior of the body or enter the body from without. The character
of the disease which appeared in epidemic form, the "Genius
epidemicus," was determined not by differences in the intrinsic cause,
but by the type of constitution which prevailed at that time. The
first epidemic of cholera which visited Europe in 1830-37 was for the
most part referred to the existence of a peculiar epidemic
constitution for which various causes were assigned. It was only when
the second epidemic of this disease appeared in 1840 that the
existence of some special virus or poison which entered the body was
assumed.

Meanwhile, by the study of the material of disease knowledge was being
slowly acquired which had much bearing on the causes. The first
observations which tended to show that the causes were living were
made by a learned Jesuit, Athanasius, in 1659. He found in milk,
cheese, vinegar, decayed vegetables, and in the blood and secretions
of cases of plague bodies, which he described as tiny worms and which
he thought were due to putrefaction. He studied these objects with the
simple lenses in use at that time, and there is little doubt that he
did see certain of the larger organisms which are present in vinegar,
cheese and decaying vegetables, and it is not impossible that he may
have seen the animal and vegetable cells.

The first description of bacteria with illustrations showing their
forms was given by Loewenhoeck, a linen dealer in Amsterdam in 1675.