in several ways: the contents of the jar might not have been
boiled for a sufficient length of time to kill all the germs, or
the air might not have been excluded completely by the sealing
process. To cover both these contingencies, Spallanzani first
hermetically sealed the glass vessels and then boiled them for
three-quarters of an hour. Under these circumstances no
animalcules ever made their appearance--a conclusive
demonstration that rendered Needham's grounds for his theory at
once untenable.[2]

Allied to these studies of spontaneous generation were
Spallanzani's experiments and observations on the physiological
processes of generation among higher animals. He experimented
with frogs, tortoises, and dogs; and settled beyond question the
function of the ovum and spermatozoon. Unfortunately he
misinterpreted the part played by the spermatozoa in believing
that their surrounding fluid was equally active in the
fertilizing process, and it was not until some forty years later
(1824) that Dumas corrected this error.


THE CHEMICAL THEORY OF DIGESTION

Among the most interesting researches of Spallanzani were his
experiments to prove that digestion, as carried on in the
stomach, is a chemical process. In this he demonstrated, as Rene
Reaumur had attempted to demonstrate, that digestion could be
carried on outside the walls of the stomach as an ordinary
chemical reaction, using the gastric juice as the reagent for
performing the experiment. The question as to whether the stomach