f the scientific progress of this century which omits the
name of Louis Pasteur would be lamentably incomplete. In that part of
science which relates strictly to human life and the means of
preserving it, the work of this great man must be placed in the first
rank. Indeed, we believe that no other stride in biological
investigation from the beginning of time has been so great in its
immediate and prospective results as has been the increment
contributed by Pasteur and his contemporary Koch. The success of these
two experimental philosophers grew out of the substitution of a new
theory for one that had hitherto prevailed respecting some of the
fundamental processes in living matter.

Up to about the close of the third quarter of this century, the belief
continued to prevail in the possibility of the propagation and
production of germ life without other germ life to precede it. It was
held that fermentation is not dependent upon living organisms, and
that fermentation may be excited in substances from which all living
germs have been excluded. This belief led to the theory of
_abiogenesis_ so-called--a term signifying the production of life
without life to begin with.

The question involved in this theory was hotly debated by philosophers
and scientists in the Sixties and Seventies. The first great work of
Pasteur in biological investigation was his successful demonstration
of the impossibility of spontaneous generation. About 1870, he became
a careful experimenter with the phenomena of fermentation. As his work
proceeded, he was more convinced that fermentation can never occur in
the absence and exclusion of living germs; and this view of the
deep-down processes in living matter has now been accepted as correct.

The next stage in the work of Pasteur was the discovery that certain
substances, such as glycerine, are products of fermentation. From this
foundation firmly established he passed on to consider the phenomena
of disease. He had been, in the first place, a teacher in a normal
school at Paris. In 1863, when he was thirty-nine years of age, he was
a professor of geology. Afterward he had a chair of chemistry at the
Sorbonne. In 1856 we find him experimenting with light, and after that
he turned to biological investigations. This led him to the results
mentioned above, and presently to the discovery that the contagious
and infectious diseases with which men and the lower animals are
affected are in general the re