PRACTICAL APPLICATIONS 419 



reasonable to suppose that there is a fair amount of immunity 

 inherent in all the tissues except in the nervous structures, and 

 that the living virus deposited elsewhere may be entirely destroyed 

 by bacteriolysis or phagocytosis. 



We have already glanced briefly at Pasteur's earlier work on 

 antirabic inoculations, and the method by which immunity is 

 produced. Numerous modifications of the process have been 

 introduced since Pasteur's time. Thus Hogyes of Budapest 

 makes use of fully virulent cords, but given in extremely small 

 doses ; and there is some reason to think that his process does 

 not really differ from that of Pasteur, and that in drying the cords 

 the virus is gradually destroyed and not really attenuated, so that 

 a dose of a fourteen-day cord really contains a small trace of 

 virus of full virulence. A true vaccine i.e., a virus of mitigated 

 virulence can be obtained by passage through monkeys or birds. 

 Further, though the fixed virus is so potent for rabbits, it is quite 

 possible that its virulence for man is slight or nil. Nitsch was so 

 sure of this that he injected 4 to 5 milligrammes of the fresh cord 

 subcutaneously unto himself (in the abdominal region, a part 

 comparatively poor in nerves) without evil results. 



Another method, introduced by Marie, consists in the use of injec- 

 tions of a mixture of virus and serum from an immunized animal. 

 This serum is prepared in a variety of ways, the simplest being to 

 give the virus intravenously. The animal usually employed is the 

 sheep, and the injection consists of rabid brains, hcatcclf up into a 

 fine emulsion with normal saline solution, and filtered through 

 linen. The serum prepared from animals treated in this way 

 possesses powerful ancirabic properties : when mixed with a 

 potent virus it removes entirely all harmful properties, so that it 

 is quite innocuous even on intracerebral injection. It can be 

 titrated against an emulsion of fixed virus of definite strength, 

 and by appropriate treatment a very potent serum can be obtained. 

 It is apparently quite useless in the treatment of the developed 

 disease or of an infected animal, even before the development of 

 symptoms. If it is mixed in excess with fixed virus and injected 

 into animals these do not develop rabies ; on the other hand, but 

 little immunity is produced, and this is supposed to be due to the 

 fact that the virus is so quickly absorbed that it does not act as 

 an antigen. But if the mixture be allowed to stand for some 

 time, and the virus then recovered by centrifugalization and 

 washing with normal saline solution, the clot thus obtained has 



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