PROPHYLACTIC IMMUNIZATION OR VACCINATION 685 



8. All animals bitten by a rabid animal should, of course, be promptly 

 destroyed; even those bitten by a dog suspected of being rabid should 

 be destroyed or closely guarded until a definite diagnosis can be reached. 

 In England, where strict laws are enforced relative to the muzzling and 

 control of dogs, rabies is relatively infrequent, and it is especially urged 

 that similar measures be adopted and enforced in our own communities, 

 particularly during the summer months. 



Principle of the Pasteur Treatment (Active Immunization) of Rabies. 

 This method is based upon the principle of stimulating the production 

 of rabic antibodies by injecting attenuated or modified virus during the 

 period of incubation, so that the virus introduced into the wound is 

 destroyed, neutralized, or its effects neutralized, while the virus itself 

 is finally destroyed. Pasteur worked out this theory and established 

 its truth by experiments upon the lower animals before applying the 

 treatment to man. 



By passing the virus through a series of rabbits, the period of incuba- 

 tion is shortened to about six to seven days, and at the same time its 

 pathogenicity for man is actually diminished (virus fixe). By drying 

 the tissues containing the fixed virus attenuation is secured, so that it 

 is easily possible so to modify the virus that it cannot produce rabies in 

 man, but yet is able to produce the specific antibodies. The Pasteur 

 treatment is, therefore, a process of active immunization with emul- 

 sions of a tissue (spinal cords of infected rabbits) in which the virus 

 has been attenuated by a process of drying and desiccation. The early 

 doses consist of highly attenuated cords, and succeeding doses become 

 gradually more potent,, as is usual in the technic of any method of active 

 immunization. 



Preparation of the Rabies Vaccine. As a preliminary, it is necessary 

 to prepare or obtain "virus fixe." This may generally be procured 

 from a laboratory, or may be prepared by passing street virus from the 

 medulla of a rabic cow or dog through a series of young rabbits. After 

 from 30 to 50 passages the incubation period is gradually reduced to six 

 or eight days ("virus fixe"). 



1. From an animal succumbing the day or night before, a piece of 

 the floor of the fourth ventricle measuring about 2 cm. in length is 

 emulsified in 1 c.c. of sterile bouillon, and three or four drops of this 

 emulsion are injected beneath the dura of a normal rabbit. In large 

 institutes two or more rabbits are injected daily. The inoculation is 

 quickly and easily performed by trephining a small area in the median 

 line of the forehead and injecting the emulsion beneath the dura mater 



