PART FIFTH. 



BACTERIA IN INFECTIOUS DISEASES. 



No more important question has ever engaged 

 the attention of physicians, of sanitarians, or of 

 biologists, than that which relates to the role of 

 the bacteria in infectious diseases. The practical 

 results of etiological studies, so far as the preven- 

 tion and cure of disease are concerned, are likely 

 to be much greater than those which have been 

 gained by the pathologists ; and, if the time ever 

 comes, as now seems not improbable, when we 

 can say with confidence, infectious diseases are 

 parasitic diseases, medicine will have established 

 itself upon a scientific foundation. But this gener- 

 alization, which some physicians think is justified, 

 even now, by the experimental evidence which has 

 been so rapidly accumulating during the past de- 

 cade, would, in the opinion of the writer, be prem- 

 ature in the present state of science. And, for the 

 present, it seems wiser to encourage additional 

 researches rather than to attempt to generalize 

 from the data at hand. For much of the evidence 

 offered in favor of this view is open to question ; 



