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 
