136 PHYSIOLOGY OF THE BACTERIA. 
CHAPTER II. 
DEVELOPMENT OF THE BACTERIA IN | 
DIFFERENT MEDIA. 
In studying the conditions of life and of develop- 
ment of bacteria in the different media, natural 
and artificial, in which they are met, we will con- 
sider the actions which they determine (or that 
they accompany) as particular cases of their nutri- 
tion and of their reproduction. We will con- 
stantly take, then, their normal physiology as our 
point of departure; and we will try to explain in 
this way the phenomena, so diverse, with which they 
are associated, — fermentations, putrefactions, con- 
tagion of infectious maladies, etc. 
It is especially interesting to study the réle of 
bacteria in non-nitrogenized chemical media, where 
they accompany the phenomena called fermenta- 
tion, properly so called; in nitrogenized media, 
vegetable or animal, which they transform, as a 
result of special fermentations, which constitute 
putrefaction ; in the human organism, where they 
accompany frequently, if not always, the develop- 
ment of certain affections having special charac- 
ters. This will be the object of so many para- 
graphs. 
