4 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



other microorganisms to each other must be considered 

 from the standpoint of systematic bacteriology. The re- 

 lationships between microorganisms and their environment, 

 such as the effect of heat and light upon their growth and 

 activities, and the manner in which microorganisms them- 

 selves bring about changes must also be considered. This is 

 the branch of science which may be termed physiological 

 bacteriology. The agriculturist is interested in microorgan- 

 isms present in foods, particularly in milk, and the changes 

 which are brought about in dairy products, that is, in dairy 

 bacteriology. The same is true of bacteria in the soil, or 

 soil bacteriology. He should acquaint himself with rela- 

 tionships of microorganisms to disease, particularly the 

 common diseases of animals; in other words, with medical 

 or pathogenic bacteriology. He should know something of 

 the ways in which the body resists disease. He must, there- 

 fore, study some of the phases of immunology. Finally the 

 methods by which disease-producing microorganisms are 

 spread, and the methods by which such passage from one 

 individual to another may be prevented may be considered 

 under the heading of sanitary bacteriology. 



Bacteriology as a science is of comparatively recent de- 

 velopment. It is probable that more has been accomplished, 

 more facts have been discovered relating to microorganisms, 

 since 1900 than in all previous time together. What is 

 true of bacteriology in general is even more true of agri- 

 cultural bacteriology. Practically all of our information 

 relative to this subject has been gained since 1880. 



In the development of the science of bacteriology, five 

 factors have been of major importance, namely, the 

 development of the microscope; the controversy over the 

 theory of spontaneous generation ; the controversy over the 

 germ theory of fermentation; the controversy over pleo- 

 morphism among microorganisms; and finally the contro- 

 versy over the germ theory of disease. 



