INTRODUCTION 21

air is essential to life, and that in hik fl^fsf the air was
excluded by the hermetically-sealed necks.

Schulze (1836) set the objection aside by filling a flask
only half full of distilled water, to which animal and
"vegetable matters were added, boiling the contents to
destroy the vitality of any organisms which might al-
ready exist in them, then sucking daily into the flask a
certain amount of air which had passed through a series
of bulbs containing concentrated sulphuric acid, in which
it was supposed that whatever germs of life the air might
contain would be destroyed. This flask was kept from
May to August; air was passed through it daily, yet with-
out the development of any infusorial life.

The term u infusorial life" having been used, here it
is well to observe that during all the early part of their
recognized existence the bacteria were regarded as ani-
mal organisms and classed among the infusoria.

Cagniard Latour and Schwann in the year 1837 suc-
ceeded in proving that the minute oval bodies which had
been observed in yeast since the the time of Leeuwenhoek
were living organisms—vegetable forms—capable of
growth; and when Boehm succeeded a year later in de-
monstrating their occurrence in the stools of cholera, and
conjectured that the process of fermentation was con-
cerned in the causation of that disease, the study of these
low forms of life received an immense impetus from the
important position which they began to assume in rela-
tion to medical science.

The experiments of Schwann, by proving that the
free admission of calcined air to closed vessels contain-
ing putrescible infusions was without effect, while the
admission of ordinary air brought about decomposition,
suggested that the causes of putrefaction which were in
the air were living entities.

In 1862, Pasteur published a paper uOn the Organized
Corpuscles existing in the Atmosphere," in which he
showed that many of the floating particles which he
had been able to collect from the atmosphere of his