662 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



is always virulent, as are also the salivary glands and the saliva. The 

 peripheral nerves frequently contain the virus, less commonly other glands 

 and secretions such as the tears, urine and milk. The virus has never 

 been found in the liver or spleen, or in the blood. Under ordinary con- 

 ditions, the chief source of danger is the saliva of the rabid animal, espe- 

 cially when this is introduced into a wound. 



Rabies may be recognized in a dog in one of three ways: observation 

 of the course of the disease; autopsy; inoculation of test-animals and 

 observation of the course of the disease in them. If the suspected dog is 

 chained or caged, the question of rabies may be settled in a few days, 

 for, if mad, the raging stage will be succeeded by the characteristic paral- 

 ysis and death. If the dog has already been killed, a careful autopsy may 

 show the absence of normal food from the digestive tract and the presence 

 there of abnormal ingested material, highly suggestive of rabies. Micro- 

 scopic examination* of the central nervous system is, in the hands of an 

 expert, a reliable method of diagnosis, which in this case depends upon the 

 finding of the characteristic Negri bodies in the specimen. For con- 

 firmation of the diagnosis, a portion of the brain or spinal cord, removed 

 without contamination, should be injected into the brain of test animals, 

 and the effects observed. This last test carried out by experienced 

 observers is justly regarded as the most trustworthy of all. 



THE NEGRI BODIES. The peculiar bodies found by Negri in the 

 central nervous system of rabid animals seem to occur invariably and ex- 

 clusively in this disease, and it is possible that they represent a stage in the 

 life history of the infectious agent. These bodies are especially numerous 

 in the Ammon's horn of the brain in cases of street rabies (Fig. 116). 

 They appear as round or somewhat triangular structures, in part inside the 

 nerve cells. Their size varies considerably, from i ( to 27^ in diameter, 

 the most of them being about 5^. In the interior of the Negri body smaller 

 spherical structures of variable size and number can be seen. Some careful 

 students of rabies regard these bodies as protozoa and consider them to be 

 the infectious agent. Proof of this belief is still lacking inasmuch as it has 

 not yet been conclusively shown that the Negri bodies are actually living 

 things. 



A wound inflicted by a rabid animal should be thoroughly cauterized, 

 under anaesthetic if desired, at the earliest possible moment, and this 



*For methods of demonstrating the Negri bodies, see Park, Pathogenic Bacteria and 

 Protozoa, Ed. 3, 1908, p. 608, 



