PART SECOND. 

 PHYSIOLOGY OF THE BACTERIA. 



CHAPTER I. 



DEVELOPMENT OF THE BACTERIA. 



The 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 



