PART FIRST. 

 MORPHOLOGY OF THE BACTERIA, 



CHAPTER I. 



ORGANIZATION OF THE BACTERIA. 



WHEN bacteria develop in a liquid in a suffi- 

 cient quantity, they become visible to the naked 

 eye. They appear either as a slight cloud, or 

 gathered in little masses in the liquid, or forming 

 a pellicle upon its surface, or as a deposit upon the 

 walls of the vessel and upon the objects contained 

 in the liquid. However, we must hasten to say 

 with M. Cohn, that the fact of the absence of all 

 turbidity in a liquid does not exclude the possi- 

 bility of the presence of bacteria. In liquids more 

 dense than water (serum, lymph, etc.), when the 

 refractive power of these corpuscles is the same as 

 that of the liquid, their presence may not be 

 revealed to the naked eye. We will add that 

 sometimes their color serves to indicate their 

 presence in a liquid, although this color is often 

 very feeble, and can only be perceived when a 

 considerable thickness of the liquid is examined. 

 If we examine these clouds, these accumulations, 

 these deposits, with the microscope, we see that 



