870 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



the virus (street virus) kills rabbits in from two to four weeks, but after 

 repeated transfer from rabbit to rabbit in series, the period of incuba- 

 tion is shortened until death occurs quite regularly in six or seven days 

 after inoculation. Beyond this there is no further increase in virulence 

 for rabbits, and this six- or seven-day virus is called the "fixed virus." 



The localization of virus in the body of the rabid animal has been 

 worked out by experimental inoculations. The central nervous system 

 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 

 conditions, the chief source of danger is the saliva of the rabid animal, 

 especially when this is introduced into a wound. 



Rabies may be recognized in a dog in one of the three ways : observa- 

 tion 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 character- 

 istic paralysis 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. Microscopic 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 confirmation 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 exclusively in this disease, and it is probable that they represent 

 stages in the development of the infectious agent. These bodies are 

 especially numerous and most easily demonstrated in the Ammon's 

 horn of the brain in cases of the natural disease in dogs (street rabies) . 

 Excellent results may be obtained by the method of Lentz.* 



Lentz, Otto, Ein Beitrag zur Faerbung der Negrischen Koerperchen, Centralbl. f. Bakt. 

 etc., I Abt., Bd. XLIV, pp. 374-378. 



