SOME COMMUNICABLE DISEASES 353 



the incubation period of a given disease is the same for animals 

 of the same species when subjected to the same mode of infection. 



ANTHRAX 



Anthrax is one of the most widespread diseases of a communi- 

 cable nature. It usually occurs as a sporadic disease in nearly all 

 warm-blooded animals and especially in cattle. The disease in 

 man chiefly occurs among those working with hides, wool, or meat 

 of infected animals. The period of incubation is from one to five 

 days. The mortality is variable, depending upon the virulence 

 of the outbreak, and runs from 50 to 95 per cent. 



Cause. — This infection is caused by the anthrax bacillus, which 

 is found in the soil, on forage, and in stagnant water. It forms 

 spores that are very resistant. A small quantity of dried soil, 

 which had been kept for eighteen years in a laboratory, has been 

 found capable of producing death when inoculated into a rabbit. 

 The germ gains access to the body through the digestive or respir- 

 atory tracts or through wounds in the skin. Infection from the 

 soil is a more frequent source of the disease than contact with 

 infected animals. The disease is communicable during the 

 febrile stage and until the lesions have ceased discharging. 

 Infected soil, water, hair, hides, etc. may remain infective for 

 many months, unless disinfected. 



Symptoms. — The most characteristic features of anthrax are 

 the suddenness of its appearance, high fever, great prostration, 

 and fatality. When the skin is affected carbuncles develop. 

 If the animal recovers, the affected skin and subcutaneous tissue 

 slough away leaving an open wound that heals slowly. 



A postmortem examination shows tar-like blood, greatly 

 enlarged spleen, congested lymphatic glands, and blood extrava- 

 sations throughout the body. The disease is identified by 

 a microscopic examination of the blood, in which the large rod- 

 shaped bacilli are found in great numbers. Animal inoculations 

 and cultural studies are used to make the diagnosis positive. 



Treatment. — As treatment of affected animals is usually not 

 satisfactory, much importance attaches to the prevention of this 

 disease. In addition to precautions for guarding the food and 

 water against contamination there are a number of methods of 

 producing immunity. The most generally used method was 



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