58 LOUIS PASTEUR 



unknown. They were among the many other in- 

 teresting and curious forms of minute life whose 

 study occupied the attention of a few naturalists. 

 Now there are departments of bacteriology with 

 their several courses in most universities and 

 medical schools. Government bureaus, agricultural 

 experiment stations, institutes for medical research, 

 and many private industrial firms are carrying on 

 investigations in this field. A small army of in- 

 vestigators devote themselves to such subjects as 

 the bacteriology of milk, the bacteriology of water, 

 soil bacteriology, dairy bacteriology, and the bac- 

 teriology of sewage, to say nothing of the bac- 

 teriology of plant and animal diseases. Almost all 

 of the enormous development of bacteriology with 

 its numerous ramifications has taken place in the 

 last fifty years. What strides may be made in the 

 next half century we can only vaguely conjecture. 

 I have said a little concerning the relation of 

 bacteria to disease. This topic, which is of the 

 greatest importance for our human welfare, will 

 occupy us more or less in the succeeding pages. 

 There is one fact in regard to bacteria, however, 

 which is of fundamental significance in relation to 

 disease as well as to other practical aspects of bac- 

 teriology, and which has come to be established 



