612 RABIES AND THE NEGRI BODIES 



to the region where the infection by bites occurred. Hellman and 

 Marx have shown that if virus is carefully injected into the peritoneal 

 cavity in such a manner that nerves are not injured, infection does 

 not occur. Intravenous injection leads to infection in dogs and rabbits 

 but not in herbivora, which shows that the possibility of infection 

 through the blood current cannot be denied, but everything points to 

 the peripheral nerves as the common routes by which the virus usually 

 travels to the central nervous system. 



Immunization in Rabies. The first attempts to immunize animals 

 were made in 1881 by Gaultier, who injected saliva from rabid dogs 

 into the jugular veins of a number of sheep and one horse. This 

 procedure did not produce rabies in the animals so treated, and, 

 according to the claim of the experimenter, protected them against 

 subsequent bites from hydrophobic dogs. Nocard and Roux repeated 

 Gaultier's experiments on sheep, goats, cattle, and horses, but instead 

 of using saliva they employed for the intravenous injections emulsions 

 from the central nervous system, and they confirmed the observation 

 of their predecessor, that such treatment produced immunity against 

 subsequent intraocular inoculation and against the bites of rabid 

 animals. 



The Pasteur Treatment. Between the experiments of Gaultier and 

 those of Nocard and Roux, Pasteur had taken up the work of immu- 

 nization against rabies. He had previously discovered the method 

 to immunize animals against fowl cholera, hog erysipelas, and anthrax 

 by the use of attenuated cultures or viruses, and he based his experi- 

 ments on rabies from the start upon attempts to prepare an attenuated 

 virus. He first succeeded in obtaining it by repeated passages through 

 monkeys. If a virus so obtained was injected subcutaneously into 

 dogs it did not produce hydrophobia and protected the animals so 

 treated against the subsequent bites of rabid dogs. The method 

 on which the so-called Pasteur treatment of hydrophobia is based 

 was subsequently worked out by Pasteur, Chamberland, and Roux. 

 Its principle is the following: Rabbits are first inoculated subdurally 

 from the virus obtained from dogs which have developed rabies. 

 This is the so-called street virus. It is of variable virulency and 

 produces hydrophobia in rabbits after a variable period of incubation. 

 If the virus is then passed on from rabbit to rabbit, always by sub- 

 dural inoculation, the period of incubation is more and more shortened 

 on account of the increasing virulency of the living poison. After 

 a number of passages the virulency reaches a certain maximum 

 beyond which it cannot be increased, and the period of incubation 

 becomes stationary at six to seven days. The virus so obtained, 

 which also shows an increased virulency when inoculated subdurally 

 into animals other than rabbits, is known as the fixed virus. It can 

 be attenuated by a variety of methods, but the method first employed 

 by Pasteur and still used by many consists in exposing the spinal 

 cords of rabbits which contain the fixed virus to drying-out processes. 



