8l6 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



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 

 n6ver been found in the liver or spleen, or in the blood. Under ordinary 

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

 especially when this is introduced into a wound. 



Rabies may be recognized in a dog in one of the three w^ys: 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 iliay 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 Negm 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.* 



Transverse sections, 2 to 3 mm. in thickness, of the Ammon's horn of the sus- 

 pected brain are hardened in acetone at 37° for one hour, then transferred to 

 melted paraffin (melting point 55°) in the paraffin oven at 38° for one and one-half 

 hours and embedded. Sections, 2 to m in thickness, are then cut with the micro- 

 tome, floated upon lukewarm water and mounted upon perfectly clean flamed 

 glass slides. The excess of water is carefuUy removed wifli filter paper and the 

 slides are then completely dried on a warm plate at 45° or in the incubator at 



• Lentz, Otto, Bin Beitrag zur Paerbung der Negrisohen Koerperchen, Centralbl. f. Bakt 

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



