DISEASES OF GOATS, DOGS, AND CATS 649 



for typhoid fever, tuberculosis, or any other infectious disease to 

 develop spontaneously. Rabies is an infectious disease and can be 

 produced only by inoculation with the specific virus which causes it. 

 This specific virus is present in the saliva of animals affected with 

 the disease and is transmitted to other animals and persons by the 

 saliva on the teeth of such animals. 



Period of Incubation. The period of incubation of rabies 

 varies within wide limits, being more or less different in the various 

 species of the animals. It also differs in the same species, depending 

 on several important factors, as the location of the bite, the char- 

 acter of the bite, and the amount of the virus injected. Bites about 

 the head, face, and hands in human beings are the most serious be- 

 cause these parts are the most exposed. The clothing on other parts 

 of the body tends to wipe the saliva from the teeth, and thus pre- 

 vents it from inoculating the wound. Bites about the face and head 

 are also more dangerous than on other parts because they are so 

 thickly supplied with nerves and the distance the virus has to travel 

 to reach the central nervous system is short. Through experimenta- 

 tion it has been pretty definitely proved that the virus travels along 

 the course of the nerves rather than by means of the blood current. 

 Deep, penetrating, or lacerating bites are obviously of greater import 

 than superficial scratches, as more virus enters the former wounds 

 and they are difficult or impossible to cauterize completely. Severe 

 hemorrhage from the wound is favorable, as there is a possibility of 

 part or all of the virus being thus mechanically removed. Infection 

 and suppuration of the wound may also destroy the virus. None 

 of these conditions, however, can be depended upon, but they ac- 

 count for the fact that a considerable proportion of persons and 

 animals bitten do not contract the disease even when no treatment 

 is given. 



The shortest period of incubation is six days in the rabbit. 

 This short period can only be obtained with what is known as "fixed 

 virus" obtained in the laboratory by repeated passage of the ordinary 

 virus through a long series of (50) rabbits. The disease as contracted 

 from the bite of a rabid dog requires an incubation period of from 

 fifteen to ninety days. At times this incubation has been prolonged 

 greatly in excess of the above figures. In one case which came 

 under the observation of this laboratory a dog belonging to one of 

 the District fire companies was bitten by a rabid dog which was ex- 

 amined by the Bureau. The animal, being a great pet, was not 

 killed and remained normal for exactly one year, when it came down 

 with a typical case of rabies which was proved by microscopic ex- 

 amination and rabbit inoculations. Such a long incubation period, 

 however, is so extremely rare that it is usually not considered in 

 formulating quarantine laws for the prevention of the disease. 

 Shorter periods of incubation than fifteen days have been reported, 

 but they are very unusual. 



Symptoms of Rabies in the Dog. The symptoms are generally 

 described under two types, the furious or irritable and the dumb or 

 paralytic. The latter type is always seen in the terminal stages of 



