906 DISEASES CAUSED BY FILTRABLE VIRUS 



poliomyelitis. After several generations large highly refractile 

 bodies with dark central spots appeared in the cultures, and these 

 Noguchi 29 regards as possibly the parasites and similar to Negri 

 bodies. Opinions are still divided as to the significance of Noguchi's 

 results. However, whatever may be one's opinion regarding the 

 nature of the peculiar bodies visible in his cultures, he has accom- 

 plished the feat of preserving the virulence of the virus through 

 twenty-one generations on artificial media, a fact which alone would 

 seem to prove that he had successfully cultivated it, even though his 

 " nucleated bodies" do not eventually turn out to be anything more 

 than cell degenerations. The possibility that he may have carried 

 original virus through twenty-one generations and that it has 

 remained virulent for about 100 days at 37.5 C. can not be excluded 

 as yet, but seems very remote. 



The Specific Therapy of Rabies. The treatment which is now 

 prophylactically applied to patients infected with or suspected of 

 infection with rabies has been but little altered either in principle 

 or in technical detail since it was first worked out by Pasteur. In 

 principle it consists of an active immunization with virus, attenuated 

 by drying, administered during the long incubation period in doses 

 of progressively increasing virulence. 



By the repeated passage of street virus through rabbits, Pasteur 

 obtained a virus of maximum and approximately constant virulence 

 which he designated as virus fixe. By a series of painstaking experi- 

 ments he then ascertained that such virus fixe could be gradually 

 attenuated by drying over caustic potash at a temperature of about 

 25 C., the degree of attenuation varying directly with the time of 

 drying. Thus, while fresh virus fixe regularly caused death in rabbits 

 after six to seven days, the incubation time following the inoculation 

 of dried virus grew longer and longer as the time of drying was 

 increased, until finally virus dried for eight days was no longer 

 regularly infectious and that dried for twelve to fourteen days had 

 completely lost its virulence. 



The method of active immunization which Pasteur used consisted 

 in injecting, subcutaneously, virus of progressively increasing viru- 

 lence, beginning with that derived from cords dried for thirteen days 

 and gradually advancing to a strong virus. Thus the patient was 

 immunized to a potent virus several weeks before the incubation time 



28 Noguchi, Jour. Exp. Med., xviii, 1913. 



