in 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.
The fineness of the linen being determined by the number of threads in
a given area, it is necessary to examine it with a magnifying lens,
and he succeeded in perfecting a simple lens with which objects
smaller than had been seen up to that time became visible. It must be
added that he was probably endowed with very unusual acuteness of
vision. He found in a drop of water, in the fluid in the intestines of
frogs and birds, and in his evacuations, objects of great minuteness
which differed from each other in form and size and in the peculiar
motion which some of them possessed. In the year 1683 he presented to
the Royal Society of London a paper describing a certain minute
organism which he found in the tartar of his teeth. After these
observations of Loewenhoeck became known to the world they quickly
found application in disease, although the author had expressed
himself very cautiously in this regard. The strongest exponent of the
view of a living contagion was Plenciz, 1762, a physician of Vienna,
basing his belief not only on the demonstration of minute organisms by
Loewenhoeck which he was able to verify, but on certain shrewdly
conceived theoretical considerations. He was the first to recognize
the specificity of the epidemic diseases, and argued from this that
each disease must have a specific cause. "Just as a certain plant
comes from the seed of the same plant and not from any plant at will,
so each contagious disease must be propagated from a similar disease
and cannot be the result of any other disease." Further he says, "It
is necessary to assume that during the prevalence of an epidemic the
contagious material undergoes an enormous increase, and this is
compatible only with the assumption that it is a living substance."
But as is so often the case, speculation ran far ahead of the
observations on which it is based. There was a long gap between the
observations of Loewenhoeck and the theories of Plenciz, justified as
these have been by present knowledge. In the spirit of speculation
which was dominant in Europe and particularly in Germany in the latter
half of the eighteenth and the first half of the nineteent