490 



VETERINARY BACTERIOLOGY 



structure and staining qualities, as shown especially by the smear 

 method of examination, resemble that of certain known protozoa, 

 notably of those belonging to the suborder Microsporidia." 



The Negri bodies in suitably stained preparations are found 

 to vary in size from less than 0.5 to 25 p. In shape they may bo 

 spherical, ovoid, or ellipsoidal. The bodies show a characteristic 

 structure, a smooth hyaline margin, with inclusions of various 

 kinds that resemble chromatin granules. 



They may be readily stained by Giemsa's method, or with 

 eosin and methylene-blue. 



Fig. 212. A Negri body. Note the circle of chromatoid granules about the 

 central body (X 2000) (Williams and Lowden). 



Pathogenesis. The organism enters the body through wounds, 

 usually bites of animals. It then passes slowly along the per- 

 ipheral nerves to the central nervous system. The portion of 

 this to which these nerves directly lead is the most seriously 

 affected. Characteristic gross anatomical lesions are quite lacking 

 in this disease. 



The period of incubation is variable; it is usually several 

 weeks. It probably represents the period necessary for the virus 

 to reach the central nervous system and develop there. The dis- 

 ease is commonly fatal. It affects most mammals, including man, 

 but is primarily a disease of the carnivora, particularly the dog. 



Immunity. The Pasteur method of treatment is essentially a 



