100 ESSAYS ON BACTEEIOLOGY. 



onism to smallpox is likewise a peculiar, isolated fact, 

 an exotic in the field of pathology. The other, that 

 it is simply smallpox in the cow, and vaccination sim- 

 ply the induction of a modified form of smallpox. 

 Either of these theories might be true and yet the pro- 

 tective influence of vaccination not excite, in this day, 

 great incredulity among scientific men. For, sup- 

 posing the former theory correct, it has been shown 

 that there is an antagonism between certain distinct 

 bacteria, an antagonism so pronounced as to be inhib- 

 itory or destructive. Thus the intensely malignant 

 anthrax is prevented or arrested by simultaneous inoc- 

 ulation with the comparatively harmless bacillus pro- 

 digiosus. There are other antagonisms of a similar 

 character, though perhaps none equally striking. It 

 is, therefore, quite within reason, and within the 

 sphere of analogy, to suppose that cowpox, being a dis- 

 tinct disease, might protect from smallpox. 



But credible though it may be, and quite within 

 the range of possibility, there seems really little noAv 

 left in support of this theory of cowpox. The facts 

 of nature, i. e., the natural history of cowpox, the in- 

 creased knowledge of recent years in the whole field 

 of bacterial pathology, and direct experiment, com- 

 bine to strengthen the view that cowjdox is simply 

 bovine smallpox. 



If this is true, the whole matter becomes a simple 

 one. 



Disco\ered accidentally, but worked out by the 



