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if injected directly into the blood, while in solid tissues the 

 same culture produces fatal results, according to the 

 experiments of MM. Arloing, Cornevin, and Thomas. The 

 law which M. Paul Bert has deduced from such observations 

 is, that any condition which arrests the development of a 

 virus converts it into a vaccine, and this implies the 

 principle that specific microbes thrive better, or attain their 

 maximum virulence, in certain tissues or juices, and are 

 attenuated in others. Most remarkable series of observations 

 have been made with respect to the varying effects from 

 harmlessness to fatality of special microbes in different 

 animals. These have led Pasteur and his assistants, MM. 

 Chamberland and Roux, to the idea that differences of 

 temperature affect the vigour of the microbes, and thermal 

 conditions have been employed as a means of attenuation in 

 the production of protective cultures. Thus the usual 

 immunity of birds against anthrax inoculations is attributed 

 by Pasteur to the high temperature of their blood, and he 

 claims to have developed anthrax in the fowl by keeping its 

 body in cold water. We must not, however, overlook, nor 

 does Pasteur overlook, the possibility of the variation in the 

 susceptibility, or vigour, being not on the side of the microbe, 

 but on the side of the animal. Thus Koch claims to have 

 developed anthrax in birds in spite of their high temperature, 

 and he suggests that the fowl in Pasteur's experiment fell 

 a victim, not because of any change in the microbe, but 

 because the fowl's own vitality was lowered, weak animals 

 succumbing to ailments which in health they would success- 

 fully throw off. These views distinctly admit the idea of 

 a definite struggle for existence between the microbe and 

 the cells of the living animal. Pasteur's views as to the 

 influence of a few degrees more or less of heat on the 

 specific vitality of the microbe are, however, supported by 

 the experiments of Willems, and later of Arloing, Cornevin, 

 and Thomas on the development of inoculations in different 



