152 THE SCIENCE OF BIOLOGY 



antiseptics was the outcome. Infection came to be the 

 mark of a bungling surgeon or a rare accident. Subse- 

 quently, the methods of antisepsis have been in part re- 

 placed by those of asepsis and by methods which enable the 

 natural bodily processes to destroy the germs that may 

 find entrance. 14 



The work of Koch (1843-1910) is representative of in- 

 vestigations which established the principles of treatment 

 and diagnosis now universal for infectious diseases. His 

 discovery (1882) of the bacillus of tuberculosis was epoch- 

 making. Bacteriology came into existence as a distinct 

 science during the last quarter of the nineteenth century, 

 when a long list of diseases were found either to be caused 

 by recognizable germs or to behave in such a fashion as to 

 indicate germinal causation. With the confirmation of the 

 mosquito-malaria theory, an important disease was shown 

 to be caused by a protozoon. During the last twenty-five 

 years, the list of such infections has been so rapidly extended 

 that protozoa have assumed an importance second only to 

 bacteria as disease-producing organisms. The important 

 role of insects, like mosquitos and house-flies, in the trans- 

 mission of disease has been discovered within the same 

 period. The immediate application of such knowledge in 

 medical practice renders these discoveries matters of com- 

 mon information. 



The germ-theory thus brought revolutionary develop- 

 ments within the two main branches of medical science. 

 Surgery and the treatment of disease became established on a 

 new basis, because of the comparatively simple discovery 

 that many diseases and the decay of organic matter are alike 

 caused by the activities of microscopic organisms. Not all 

 diseases are so caused, and the germs of certain infectious 



14 The story is vividly presented by the veteran American surgeon W. W. 

 Keen, "Before and after Lister," Science, June 11, 1915. See also: 

 "Medical Research and Human Welfare," by the same author; and the 

 essay by O. W. Holmes on "Puerperal Fever." 



