THERAPEUTIC IMMUNIZATION IN MAN 489 



removed, not only for humane reasons, since the same object might 

 be attained with anesthesia, but because a thorough autopsy can then 

 be performed to determine the health of the calf. 



Vaccines so obtained always contain bacteria, the glycerin there- 

 fore serving a double purpose : one, the preservation of the virus, the 

 other a gradual destruction of the bacteria. Kosenau has shown that 

 the addition of 2 to 4 parts of 60 per cent, glycerin to one part 

 weight of the pulp prevents the growth of bacteria and probably 

 destroys them by dehydration. Most of the bacteria are destroyed 

 within one month at 20 C. During this period, then, from 4 to 6 

 weeks, the glycerinated virus should not be used, and should from 

 time to time be controlled by cultivation. At the end of this time 

 the lymph is ready for use. 



Formerly the material for the vaccination of human beings was 

 obtained very simply by dipping ivory splinters into the fluid of pus- 

 tules, allowing this to dry, and rubbing these ivory or bone points 

 into the exudate obtained by scratching the skin of the individual to 

 be vaccinated. This method has practically gone out of use, and 

 to-day the ripened glycerin pulp prepared as above is taken up in 

 small capillary glass tubes and from these blown upon the vaccina- 

 tion scratch. The efficiency of vaccine virus can be tested for po- 

 tency by the inoculation of the ears of rabbits before use. 



ACTIVE PROPHYLACTIC IMMUNIZATION IN RABIES (HYDROPHOBIA) 



Although many modifications have been suggested and actually 

 used in different parts of the world, the most common method of 

 immunizing against rabies still remains that originally devised by 

 Pasteur. The Pasteur treatment takes advantage of the prolonged 

 incubation period of rabies and is planned to confer immunity be- 

 tween the time of inoculation and the time at which the disease 

 would naturally appear. Since this period in ordinary street infec- 

 tion by dog bite is usually 40 days or more, a considerable interval 

 for active immunization is available. Formerly much of this time 

 was lost in that the diagnosis of hydrophobia in the dog or other 

 animal that had caused the injury could not be made with certainty 

 until the results of rabbit inoculations had been obtained. Nowadays 

 the ease with which a diagnosis of hydrophobia can be made within 

 a few minutes by finding negri bodies in the hippocampal and cere- 

 bellar cells has added considerably to safety in that it has made pos- 

 sible a gain of almost two weeks in determining whether treatment 

 should be instituted or not. 



Here again, although the infectious agent of rabies is not known 

 with certainty even at the present day, the method of Pasteur de- 

 pends upon active immunization by means of an attenuated virus. 



In standardizing the virus for the purpose of treatment Pasteur 

 first produced what he calls the "virus fixe." This consists of the 



