376 THE POPULAR SCIENCE MONTHLY. 



gate the subject, and from their labors we shall by-and-by be in pos- 

 session of the first really accurate and scientific examination of the 

 effects of volcanic eruptions, which in this case bids likely to result, 

 to meteorological science at least, in a gain whose immense importance 

 it is impossible now to calculate. Nor is it unlikely that this " biggest 

 terrestrial experiment " afforded us by Kature may ultimately prove 

 to have been not the least of her beneficent gifts to humanity. — Pro- 

 ceecUngs of the Royal Geographical Society, 



THE PKEYENTION OF HYDEOPHOBIA.* 



By M. LOUIS PASTEUR. 



THE important fact that certain viruses may be varied in potency, 

 and that protection against one may be afforded by another less 

 potent, is to-day not only gained for science, but has entered the stage 

 of application. It is obvious that great interest attaches, in pursu- 

 ing this line of study, to the investigation of methods of attenuation 

 adapted to new virus. I announce to-day an advance thus made in 

 regard to rabies. 



In passing from a dog to a monkey, and then from one monkey to 

 another, the potency of rabies- virus decreases at each transfer. After 

 its strength has been thus diminished, if the virus is then transferred to 

 a dog, a rabbit, or a Guinea-pig, it still remains attenuated. In other 

 •words, it does not regain all at once the intensity of virus from a mad 

 dog. Only a small number of transfers from monkey to monkey is 

 necessary to bring the virus to such a state of attenuation that it will 

 not induce madness in a dog when introduced hypodermically. Even 

 inoculation by trepanning, that most certain method of communicating 

 rabies, will produce no result except that of causing in the animal a 

 condition of insusceptibility to rabies. 



The potency of rabies-virus increases in passing from one rabbit 

 to another, or from one Guinea-pig to another. When it has been 

 brought to a maximum in rabbits, it exhibits its full strength on being 

 transferred to the dog, and is then more potent than virus from a mad 

 dog. Such virus inoculated into the circulatory system of a dog in- 

 variably causes madness which results in death. 



Although the virus rises in potency at each transfer from rabbit 

 to rabbit, or from Guinea-pig to Guinea-pig, it must pass through sev- 

 eral of these animals in order to regain its maximum potency, when 

 this has first been reduced in monkeys. In like manner, the virus of 



* Communicated to the Academy of Sciences, May 19, 1884, by M. Pasteur and MM. 

 Chamberland and Roux. 



