OUTSTANDING BIOLOGICAL ADVANCES 25 



was inevitable that some minute animal organisms 

 also should become involved. This overlapping of 

 closely related fields of investigation is so common 

 that it may be accepted as characteristic. 



For our present purpose we shall not take up 

 specifically the various topics, mentioned above, 

 but, under the general caption Bacteriology, treat 

 in a general way of the movement and its re- 

 sults. 



Rise of Bacteriology. The rise of bacteriology 

 with its germ-theory of disease had far-reaching 

 consequences for the benefit of mankind; there is, 

 in fact, no biological advance that has had more 

 important bearings on the welfare of the human 

 race. 



The micro-organisms are so minute that one would 

 scarcely expect them to play an important part in 

 human affairs. The world of exceedingly minute 

 life was first exposed by the Dutch microscopist, 

 Leeuwenhoek, who, in 1675, discovered the protozoa 

 and, in 1683, the bacteria. The protozoa are micro- 

 scopic animals while the bacteria are microscopic 

 plants. The more general term micro-organisms is 

 convenient as it includes them both and, of course, 

 other minute plants that are not bacteria. It was 



