INTRODUCTION. 



By a process of adaptation and growth, the branch of science commonly 

 recognized as "Bacteriology" has for many years included, besides 

 the bacterial forms, those microorganisms yielding to the same laboratory 

 methods of study and investigation. This is a policy or purpose instituted 

 by Pasteur. It is also the result of investigations and added knowledge, 

 more definite arrangements of available facts, and the highly specialized 

 training required for the work. In short, technic together with the eco- 

 nomic relations of the subject-matter has no little influence in placing 

 limitations. In the light of such circumstances, it appears more pertinent 

 to designate this text-book as "Microbiology," perhaps not the best term, 

 but one much in accord with French usage. 



Agriculture, Domestic Science and certain other courses in scientific 

 schools and colleges call for the treatment of the subject in such a man- 

 ner as to make it basic to the interpretation of such subjects as air im- 

 purities, water supplies, sewage disposal, soils, dairying, fermentation 

 industries, food preservation and decomposition, manufacture of biolog- 

 ical products, transmission of disease, susceptibility and immunity, sani- 

 tation, and control of infectious or contagious diseases. A strong effort 

 has been made to provide the fundamental and guiding principles of the 

 subject and to show just how these principles fit into the subjects of a 

 more or less strictly professional or practical nature. Here the instruc- 

 tional work of the microbiologist stops in most educational institutions 

 and the instruction of the practical or professional man begins. 



Because of the extreme massiveness and diversity of the subjects, 

 Agriculture and Domestic Science and Industrial Vocations in general, 

 a comprehensive consideration of the subject is demanded. Elimination 

 of many features not only becomes difficult but really precarious, because 

 so many avenues are open to the student that pertinency cannot always 

 be foreseen or determined. It is well to remember, too, that such aggre- 

 gate subjects as Agriculture and Domestic Science, unlike Engineering 

 and Medicine, because of their youth, have not developed to that stage 







VII 



