614 HYDEOPHOBIA 



shown by inoculating an animal subcutaneously in one of its 

 limbs with virulent material. If now the animal be killed 

 before symptoms have manifested themselves, rabies can be 

 produced by subdural inoculation from the nerves of the limb 

 which was infected. Further, rabies can often be produced from 

 such a case by subdural infection with the part of the spinal 

 cord into which these nerves pass, while the other parts of the 

 animal's nervous system do not give rise to the disease. This 

 explains how the initial symptoms of the disease (pains along 

 nerves, paralysis, etc.) so often appear in the affected part of the 

 body, and it probably also explains the fact that bites in such 

 richly nervous parts as the face and head are much more likely 

 to be followed by hydrophobia than bites in other parts of the 

 body. Again, injection into a peripheral nerve, such as the 

 sciatic, is almost as certain a method of infection as injection 

 into the subdural space, and gives rise to the same type of 

 symptoms as injection into the corresponding limb. Intravenous 

 injection of the virus, on the other hand, differs from the other 

 modes of infection in that it more frequently gives rise to 

 paralytic rabies. This fact Pasteur explained by supposing 

 that the whole of the nervous system in such a case becomes 

 simultaneously affected. In certain animals the virus seems to 

 have an elective affinity for the salivary glands, as well as for 

 the nervous system. Koux and Nocard found that the saliva of 

 the|dog became virulent three days before the first appearance 

 of symptoms of the disease. 



The Virus of Hydrophobia. — While a source of infection 

 undoubtedly occurs in all cases of hydrophobia, and can usually 

 be traced, all attempts to determine the actual morbific cause 

 have been unsatisfactory. In this connection various organisms 

 have been described as being associated with the disease, but 

 none of these have been shown to possess the capacity of pro- 

 ducing immunity against the ordinary hydrophobic virus. 



The only definite information we possess regarding the causal 

 organism of rabies is that in one stage of its life-history at any 

 rate (see p. 622) it must be extremely small, as it can pass 

 through the coarser Berkefeld filters and also sometimes through 

 the coarser Chamberland filters. This is shown by the fact that 

 if an emulsion of any infective material (e.g., the brain) be thus 

 filtered, the filtrate is also infective. Evidence that it is the 

 organism itself which passes through is found in the fact that 

 when an animal dies from infectibn with the filtrate, a small 

 portion of its central nervous system will originate the disease 

 in a fresh animal. Judging from our knowledge of similar 



