No. 7. DEPARTMENT OF AGRICULTURE. 193 



greatest difficulty in demonstrating Negri bodies in the smears is 

 experienced with the specimens from the larger animals, particularly 

 the horse. The brain of the horse seemingly contains a substance 

 which interferes with the proper staining of the smears or impres- 

 sions. Then too, the distribution of the bodies in the brain of the 

 horse is not uniform ; they are apt to be localized and this fact also 

 accounts for the percentage of failure to demonstrate Negri bodies. 

 The same difficulty in the staining of smears or sections and the ten- 

 dency for the bodies to localize is met with in the hog and deer, to 

 a less extent in man, and only occasionally in cattle. 



In 127 instances in which animal inoculation tests were made 

 following the examination of the brain tissue for Negri bodies, in 

 not one of the Gl in which Negri bodies Avere demonstrated in the 

 material inoculated did the rabbits fail to develop rabies. In 86 

 in which Negri bodies were found in the material inoculated, the 

 animal inoculation test Avas negative in 52; in 14 the animal inocu- 

 lation tests proved that rabies existed. Negri bodies during 1906 

 and 1909 inclusive have been sought for in 728 cases and found in 

 512, and in 216 no Negri bodies were found. 



RULES REGULATING THE EXAMINATION AND DIAGNOSIS 



Negri bodies and the Van Gehuchten-Nelis changes make their ap- 

 pearance in the nervous system a short time before the animal shows 

 symptoms. The virus, however, may be present in the saliva and the 

 animal capable of transmitting the disease several days before symp- 

 toms are observed. From the routine examination of specimens, it is 

 seen that Negri bodies are most abundant and the Van Gehuchten- 

 Nelis changes most marked in dogs that have died a natural death. 

 In those animals destroyed early in the course of the disease, it is 

 difficult and at times impossible to demcmstrate Negri bodies or Van 

 Gehuchten-Nelis changes, although rabies exists. Therefore, the 

 rules regulating the examination and diagnosis depend upon the 

 manner in which the animal met its death. It is always desirable 

 to have this information with the specimen. 



Specimens from animals that have died a natural death, those not 

 destroyed, are examined and the diagnosis is made as follows: 



1. Smears are made and examined for Negri bodies, and as soon 

 as the bodies are found the examination is discontinued and a di- 

 agnosis of rabies is made. 



2. When Negri bodies are not found in the smears, sections of 

 those structures already examined by the smear method are examined, 

 and if Negri bodies are found the examination is discontinued and 

 a diagnosis of rabies is made. 



8. When Negri bodies are not demonstrated, the plexiform gang- 

 lion are examined for the Van Gehuchten-Nelis changes, and if ab- 

 sent a negative diagnosis is made. 



4. Where Negri bodies are not demonstrated and well marked 

 characteristic Van Gehuchten changes are found, a diagnosis of 

 rabies is made and the animal inoculation test is carried out to verify 

 the diagnosis. 



13—7—1910 



