PROTOZOA 35 



intoxication. 1 MetchnikofFs experiments have shown that 

 the high acid reaction produced by 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 production of indigo and in the 

 preparation of hides for tanning, bacterial enzymes play an 

 important part. 



Bacteria serve a useful purpose in the disposal of sewage 

 and food wastes. There is a large group of them that digests 

 organic material to a simple soluble form, reducing the bulk 

 of matter discarded by man and animals as waste, at the 

 same time destroying pathogenic germs. This last action 

 is done chiefly by robbing the disease-producing organisms 

 of oxygen and producing so much acid that life for them is 

 impossible. This is well seen in the septic tank process of 

 sewage disposal, a method of storing waste for some days 

 to allow the above processes to occur. 



The disease-producing powers of bacteria might, in a 

 philosophical sense, be looked upon as carrying out the same 

 scheme of removing a certain number of human beings and 

 animals so that the world will not become overcrowded. At 

 all events the action of bacteria in the universe is beneficial 

 in very many ways, and as an enemy they are to be looked 

 upon as only one of the many forces with which life must 

 contend, yet without which life would be impossible. 



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 



1 Auto-intoxication is a term sometimes given to this condition, but it is 

 incorrect and should be limited to disease due to some functional disorder 

 of digestion. 



