132 THE AMERICAN MONTHLY _ [May 
mulated in the standard teachings as to the cause of con- 
tageous diseases. If, for example, anthrax is caused by 
the Bacillus anthracis gaining entrance to the interior of 
the body and multiplying there, and if the disease cannot 
be produced in the absence of this bacillus, then it be- 
comes plain that the disease is not caused by electrical 
disturbances of the atmosphere, by too much food or too 
little food, by forage containing too much water or that 
which is too dry, by intense heat of summers or extreme 
cold of winters, or indeed by any of the other influences 
to which the development of the disease has been usually 
attributed. It was contact with substances containing 
the bacillus which produced the disease, and when this 
bacillus gained access to the animal body the disease de- 
veloped without reference to the atmospheric conditions, 
the food, or the other elements of the environment. 
The comprehension of this fact led Bouley and other 
great pathologists to revise their opinions regarding the 
origin of many contagious diseases. It had been held that 
glanders originated spontaneously from overwork andin- . 
sufficient food; that bovine pleuropneumonia developed 
as a result of exposure of cattle in the mountains of Eu- 
rope to extremely low temperatures ; that cattle plague 
arose spontaneously in eastern Europe, and particularly 
on the steppes of Russia, and that rabies in the dog re- 
sulted from unfavorable conditions of life. The demon- 
stration of the germ theory of contagion, which was quite 
unexpected by the majority of medical men, completely 
overturned these old views, based upon an entirely dif- 
ferent hypothesis. The idea of spontaneous development, 
of origin de nova, was generally abandoned, and the fur- 
ther scientific researches have been pushed, the more in- 
contestible does it appear that the one and only factor of 
consequence in the production of these diseases is the en- 
trance of the disease germ into the interior of the animal 
body, where it can multiply and disseminate itself. 
