RABIES 189 



RABIES. 



While the actual principle underlying the preventive vaccina- 

 tion against smallpox was scarcely recognized by Jenner and his 

 contemporaries, their work nevertheless constitutes the basis of all 

 our modern vaccine work, and to it may be directly attributed the 

 successful preventive treatment of another dreadful disease, the 

 pathogenic agent of which has likewise not yet been isolated, viz., 

 rabies. This discovery we owe to the genius of Pasteur, and to him 

 undoubtedly belongs the credit for having first recognized that by 

 the use of suitably attenuated virus full protection may be afforded 

 against the corresponding full-virulent infection. In Jenner's case 

 nature had performed the experiment for him; but Pasteur was the 

 first who purposely employed the animal experiment to demonstrate 

 the principle in question. 



The idea underlying Pasteur's antirabic treatment is to immunize 

 the bitten individual within the period of time that the actual 

 disease requires for its development. To accomplish this it was 

 necessary so to change the nature of the virus that the incubation 

 period following its injection should be materially shorter than that 

 of the actual disease, which is usually from two to three weeks, but 

 may be as long as two months, or even longer. . 



This was accomplished by passing the natural virus, or street virus, 

 as it is usually termed, through a series of fifty rabbits, when its 

 period of incubation was found to be reduced to but six to eight days. 

 Further passage does not change this, and such virus, which, more- 

 over, no longer produces the symptoms of furious rabies in dogs or 

 guinea-pigs, but merely the paralytic type of the disease, is now 

 termed vims fixe. In a certain sense, viz., insofar as the effect of 

 the animal passage upon the period of incubation is concerned, we 

 may look upon the virus fixe as being increased in virulence, but so 

 far as its pathogenic properties go there is reason to think that for 

 man this is actually diminished. Pasteur then found that the 

 virulence of the virus in question can be still further diminished by 

 desiccation, and that after twelve to fourteen days it is lost alto- 

 gether. The plan of treatment then is to inoculate the patient 

 on successive days with material of increasing virulence, beginning 

 with that which is altogether innocuous, i. e., twelve to fourteen 

 days old. 



