THE CONQUEST OF HYDROPHOBIA 211 



cause, in most cases, the time of infection is defi- 

 nitely known, whereas with such diseases as 

 diphtheria, scarlet fever, or tuberculosis people are 

 quite unconscious of when they may have picked 

 up the infection. 



Pasteur's next step was naturally that of apply- 

 ing his treatment to animals after they had been 

 infected with hydrophobia. His procedure was to 

 take two dogs and allow them both to be bitten by 

 a mad dog; one he would vaccinate; the other 

 would be left without treatment. The vaccinated 

 dogs proved to have been protected against hydro- 

 phobia, while the others commonly succumbed to 

 this disease. The immunizing process thus won in 

 its race against the slower but more deadly onset 

 of the unmodified disease. Here was a discovery 

 which could be directly applied to saving the lives 

 of animals which had been bitten by rabid dogs. 



The interest and hope kindled by this discovery 

 of a cure for hydrophobia became widespread. The 

 Emperor of Brazil wrote to Pasteur enquiring anx- 

 iously about the progress of the investigations and 

 especially when the treatment for hydrophobia 

 could be applied to man. Similar enquiries came in 

 from various other quarters, but Pasteur felt great 

 hesitancy about risking the treatment upon human 



