36 BACTERIA AND THEIR PLACE IN NATURE 



if they be the right kind they give to butter and cheese a desirable 

 flavor. They take part in the tanning of leather, the retting of flax, 

 the curing of tobacco, and, in short, they help us in a hundred and 

 one ways we little suspect. One of the most fascinating and instruc- 

 tive tasks set for man is to learn how to increase the work of the 

 beneficial bacteria and to suppress or entirely weed out the injurious 

 bacteria. 



Divisions of Bacteriology. Bacteriology, although one of the 

 youngest of sciences, is no longer confined to one branch which can 

 be adequately covered by one text or its whole field covered by any 

 one individual, but is, as are the other sciences, divided into a 

 number of divisions each dealing with a certain phase of the subject. 

 The main divisions are: 



1. Agricultural bacteriology which deals with the bacteria of the 

 soil and their relation to plant life. 



2. Dairy bacteriology which deals with the bacteria of milk and 

 their relations to dairy products such as pure milk, butter, and 

 cheese. 



3. Industrial bacteriology, which considers the use of bacteria in 

 the arts and which also deals with methods of suppressing injurious 

 bacteria and favoring the beneficial. 



4. Plant pathology which deals with the cause and prevention of 

 those diseases that attack plants by invading their tissues. 



5. Animal pathology which deals with bacteria in relation to the 

 diseases of the lower animals. 



6. Human pathology which deals with the distribution, mor- 

 phology, physiology, and pathological changes produced by bacteria 

 which are pathogenic to man. 



