. RABIES— LYSSA—HYyDROPHOBIA 421 



and in the Panama Zone, a badly infected district, good 

 results have been obtained from antitoxin used as a preven- 

 tive. The immunity produced lasts about one month. 



RABIES. LYSSA. HYDROPHOBIA. 



Definition. — ^Rabies is a contagious, generally fatal, infec- 

 tious disease, transmitted by the bite of an infected animal 

 and characterized by delirium, nervous excitement, and 

 finally paralysis. Its incubation period is very varied and no 

 characteristic macroscopic lesions are found on postmortem. 



Occurrence. — The disease is most common (80 per cent.) in 

 dogs which, when infected, inoculate by biting other animals 

 (horses, cattle, sheep, and swine) or human beings, thus 

 spreading the disease. Rabies occurs in nearly every coun- 

 try in the world. Australia is said to be free from it, and 

 since the introduction of the last muzzling law in 1895 the 

 disease has disappeared in Great Britain. Within the past 

 ten years rabies has become widespread in the United States. 

 No std,te is free from it, but accurate statistics as to its prev- 

 alency are not available. From 1900 to 1910 it was reported 

 in 73 cities, causing the death of 230 persons. 



Etiology. — ^Rabies is due to an organism which in certain 

 stages at least is ultramicroscopic and passes through bacterial 

 filters. The virus is found in the tissues and fluids of the 

 infected body, especially in the central nervous system. It 

 also occurs in the saliva, pancreatic juice and milk, occa- 

 sionally in the aqueous humor and has been found to exist in 

 the blood. The muscles seem free. In 1903 the Italian 

 investigator, Negri, discovered in the protoplasm of certain 

 nerve cells of rabid animals small, stainable bodies which are 

 now called "Negri bodies." They were demonstrated in 

 95 to 98 per cent, of the cases of rabies examined, and are 

 rarely found in old, healthy dogs (immunes). It is probable 

 that these bodies are protozoa which in some stages of their 

 development are small enough to pass through bacterial 

 filters. Of this, however, there is as yet no scientific proof 

 available. 



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