20 ESSAYS ON BACTERIOLOGY. 



have been almost constantly under discussion, for it 

 confronts us daily, as practicing physicians, and is of 

 great importance in the broader sphere of preventive 

 medicine. To illustrate: When may children re- 

 turn to school from a family in which an infectious 

 disease has been prevailing? If tuberculosis is an in- 

 fectious disease, how long does tuberculous matter re- 

 main dangerous? 



It would not be at all true nor fair to say that all 

 our present knowledge on this subject has come from 

 bacteriology; far from it. Much of it is the result of 

 that painstaking observation and study which pre- 

 vailed in 'former days. But much is the product of 

 the last few years; and in this connection it is to be 

 noted that progress of late has been upon more defi- 

 nite lines. If the infectious diseases are due to living 

 things, this question resolves itself chiefly into a study 

 of those organisms. A specific germ being identified, 

 the question, how long may the poison of this disease 

 continue as poison, becomes, how long may this germ 

 live? The investigation evidently centers at once 

 upon a more definite point. How long, then, may 

 bacteria live? The answer is: it depends upon certain 

 conditions; and it is the discovery of the germs them- 

 selves, and increasing knowledge of the conditions 

 upon which their life depends, w;hich has brought us 

 closer to a solution of this problem. 



The life and growth of bacteria depends upon the 

 soil on which they are placed, and the external influ- 



