38 GENERAL BIOLOGY 



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 presence or by 

 taking their nutriment to the damage of their host. 

 Malaria organisms, for example, may block capillaries 

 and shut off blood supply, although they also disturb 

 the nourishment of the tissues further by destroying 

 red blood cells, which carry oxygen. 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. 



