l8o THE STORY OF GERM LIFE. 



ventive inoculation has been made, but one based 

 upon a different principle. Hydrophobia is cer- 

 tainly one of the most horrible of diseases, al- 

 though comparatively rare. Its rarity would ef- 

 fectually prevent mankind from submitting to 

 a general inoculation against it, but its severity 

 would make one who had been exposed to it 

 by the bite of a rabid animal ready to submit 

 to almost any treatment that promised to ward 

 off the disease. In the attempt to discover a 

 means of inoculating against this disease it was 

 necessary, therefore, to find a method that could 

 be applied after the time of exposure i. e., after 

 the individual had been bitten by the rabid ani- 

 mal. Fortunately, the disease has a long period 

 of incubation, and one that has proved long 

 enough for the purpose. A method of inocula- 

 tion against this disease has been devised by Pas- 

 teur, which can be applied after the individual 

 has been bitten by the rabid animal. Apparently, 

 however, this preventive inoculation is dependent 

 upon a different principle from vaccination or in- 

 oculation against anthrax. It does not appear to 

 give rise to a mild form of the disease, thus pro- 

 tecting the individual, but rather to an acquired 

 tolerance of the chemical poisons produced by 

 the disease. It is a well-known physiological fact 

 that the body can become accustomed to tolerate 

 poisons if inured to them by successively larger 

 and larger doses. It is by this power, apparently, 

 that the inoculation against hydrophobia produces 

 its effect. Material containing the hydrophobia 

 poison (taken from the spinal cord of a rabbit 

 dead with the disease) is injected into the indi- 

 vidual after he has been bitten by a rabid animal. 

 The poisonous material in the first injection is 



