36 GENERAL BIOLOGY 



certain saprophytes, the lactic acid germs in particular, 

 is inimical to the producers of this disturbance. In 

 practice, therefore, cultures of these bacteria are 

 administered by mouth. 



Other activities of bacteria and their enzymes are 

 seen in the precipitation and curdling of cream, known 

 as cheese. Again, the specific flavor of tobacco and 

 opium for the pipe is due to bacteria. In the pro- 

 duction of indigo and in the preparation of hides for 

 tanning bacterial enzymes play an important part. 



Protozoa. Of the saprophytes of protozoa practically 

 nothing is known. Protozoa are parasitic either by the 

 mechanical irritation caused by their pressure or by 

 taking their nutriment to the damage of their host. 

 For optimum development they require, as in the 

 case of bacteria, moisture and a suitable reaction, 

 but rather a higher temperature and more complicated 

 food, as a rule. 



