PART SECOND. 
PHYSIOLOGY OF THE BACTERIA. 
CHAPTER I. 
DEVELOPMENT OF THE BACTERIA. 
TuE bacteria are now known to us from a mor- 
phological point of view: let us proceed to study 
the life of these microscopic beings; first, from 
a general point of view, that is to say, by study- 
ing their functions of nutrition and reproduction, 
independently of the special characters impressed 
upon these functions by certain media; then by 
considering the relations which are established 
between the bacteria and the particular media in 
which they may be developed. 
The bacteria are of all beings the most widely 
diffused. We meet them everywhere, — in the 
air, in water, upon the surface of solid bodies, in 
the interior of plants and animals. If we expose 
a transparent liquid containing traces of organic 
substances, we find after a short time that it has 
become clouded, and the microscope shows us that 
it contains myriads of these beings. 
What is the source of these organisms so widely 
disseminated, and which develop so rapidly? This 
