268 MICROBES AND TOXINS 



virus by mixing it with glycerine, so that it is no longer necessary 

 to vaccinate directly from the calf. Inflamed arms are nowa- 

 days quite the exception. 



According to certain observers there are really only two types 

 of smallpox, the pox of sheep and that of man. All the others 

 are said to be mere modifications of these two types ; for small- 

 pox is very apt to become modified in adapting itself to different 

 animal species. 



Vaccinia, in this theory, would simply be an adaptation of 

 human smallpox to cattle, and, starting with this idea, attempts 

 have been made to transform smallpox into cowpox experiment- 

 ally by inoculating from man to the calf. This question of 

 variolo-vaccinia has been very much studied and is being taken 

 up again to-day. The results obtained have been much dis- 

 cussed, and it is not yet absolutely proved that it is possible to 

 produce in the laboratory in a short time a change which 

 nature has probably required centuries to accomplish. 



Rabies. Pasteur's treatment takes advantage of the period 

 of incubation, which is on the average six weeks. The patient 

 ought to be treated as soon as possible after the bite and before 

 the appearance of symptoms. 



In the process there is inoculated the virus fixe, which is 

 kept going in the nervous system of the rabbit, is contained in 

 the spinal cord, and may be modified by drying the latter in 

 the dark at the temperature of 23. To begin with, a cord dried 

 for fourteen days is injected, and at the end of the treatment a 

 cord dried for three days. The rate of treatment varies accord- 

 ing to the site and gravity of the bites, there being three 

 formulae, the fifteen-day, eighteen-day, and twenty-one day 

 treatments. The mortality in rabies has been reduced to 0-3 

 per cent, instead of 15 to 20 per cent. 



The microbe of rabies is unknown, and Pasteur treatment 

 is one of the crowning glories of experimental medicine. 

 Consider the facts which it has been necessary to determine 

 before arriving at its application : in the first place, the virus 

 of rabies exists in the brain of rabid animals ; further, it is 

 possible to make a pure inoculation of it ; the virus of any 



