600 RABIES AND THE NEGRI BODIES 



to destroy the virus may depend on individual lack of immunizing 

 power, and sometimes on local disturbances in the central nervous 

 system. Medical literature is full of records of cases in which either 

 physical or mental shock seemed to determine the development of 

 rabies. 



Paltauf, from his studies and the observations given above, draws 

 the following summary of conclusions with reference to the behavior 

 of the virus of rabies after its entrance in natural infection into the 

 bodies of animals and persons : 



1. The period of incubation in rabies in man varies between two 

 weeks and two years and over. 



2. Dogs are evidently quite susceptible to the virus of rabies, 

 though not highly so, since about 40 per cent, of dogs bitten contract 

 the disease. 



3. Man is not very susceptible to the virus of rabies in dogs; only 

 from 6 to 9 per cent, or perhaps even a much smaller number of 

 persons bitten develop rabies, and if not properly treated early, die 

 from the disease. 



4. Of persons bitten by wolves about 60 per cent, develop rabies. 



5. There is an enormous difference between the original sus- 

 ceptibility of man to the virus of rabies in dogs and the mortality 

 in cases which have proved to be susceptible. 



6. Observations made on four persons bitten by rabid dogs and 

 who died from intercurrent diseases (not rabies) soon after the 

 Pasteur treatment was begun showed that their cords when emulsified 

 and injected into rabbits produced after long periods of incubation 

 the slow, so-called "consumptive" form of rabies. 



Paltauf does not try to explain the long period of incubation of 

 two to three years and more which has been observed in a few authen- 

 ticated cases of rabies in animals and persons. It might be explained, 

 perhaps, as follows: When animals or persons are bitten by rabid 

 dogs there may be a shorter or longer period of latency, and the 

 virus may finally be completely exterminated by the protective powers 

 of the body. On the other hand, there may occur an incomplete 

 destruction of the virus and imperfect immunity, but a continuous 

 period of latency as is found in trypanosomiasis and particularly in 

 Texas fever. In the latter disease a few piroplasmata may persist in 

 cattle without detriment to the animal until a great strain, changes 

 in environment, or intercurrent disease leads to a sudden multi- 

 plication of these organisms, with a typical explosive outbreak of the 

 disease. Likewise, it is quite possible that the rabies organisms 

 may survive for a long time in small numbers in a person bitten by 

 a mad dog, and that under certain conditions they may suddenly 

 multiply and produce a typical fatal attack of the disease. 



Symptoms in the Dog. The symptoms of rabies in the dog are 

 described by Hart as follows : 



"The symptoms are generally given for two different types, the 



