RABIES. 665 



Such a method as this, however, had several disadvan- 

 tages, and was not absolutely certain in its action, as 

 only fifteen out of twenty dogs were completely pro- 

 tected. Pasteur, therefore, assisted by Chamberland 

 and Roux, devised a more trustworthy and accurate 

 method, in which he utilized the fact that the cord of 

 a rabic animal when kept under certain conditions loses 

 its virulence in fourteen days. A series of cords cut 

 into short segments, which were held in series by the 

 dura mater, were suspended in sterile glass flasks 

 plugged with cotton stoppers, and containing a quantity 

 of some hygroscopic material, such as caustic potash; 

 and the whole was kept at a temperature of about 22 

 C. The cord when taken out at the end of the first 

 twenty-four hours was found to be almost as active as 

 the fresh untreated cord; that removed at the end of 

 forty-eight hours was slightly less active than that re- 

 moved twenty-four hours previously; and the diminu- 

 tion in virulence, though gradual, progressed regularly 

 and surely until, as already noted, at the end of the 

 fourteenth or fifteenth day the virus was inactive. An 

 emulsion of the cord of the last day was made, and a 

 certain quantity injected into a dog that had been bit- 

 ten; this was followed by an injection of an emulsion 

 of a thirteenth-day cord, and so on until the animal 

 had been injected with a perfectly fresh and, therefore, 

 extremely active cord, corresponding to the fixed virus. 

 Animals treated in this way were now found to be abso- 

 lutely protected, even against subdural inoculation with 

 considerable quantities of the most virulent virus; and 

 thus his protective inoculation against rabies became an 

 accomplished fact. As it would be impossible, how- 

 ever, or very undesirable, to inject any but persons who 



