382 DISEASES INVOLVING NERVOUS SYSTEM 



mines, where general tetanus commonly follows foot injuries, 

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

 results have been obtained from antitoxin used as a preven- 

 tative. The immunity produced lasts about one month. 



RABIES. LYSSA. HYDROPHOBIA. CANINE MADNESS. 



Definition. — Rabies is a contagious, generally fatal, in- 

 fectious 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 postmortem. 



Occurrence. — The disease is most common (80 pet 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 wide-spread in the United 

 States. No State is free from it, but accurate statistics as 

 to its prevalency 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 in- 

 fected body, especially in the central nervous system. It also 

 occurs in the saliva, pancreatic juice and milk, occasionally 

 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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