304 ACUTE GENERAL INFECTIOUS DISEASES 



Natural Infection. — (a) Digestive Tract. — In animals the 

 usual mode of infection is through the digestive tract, the 

 spores being taken in with the food and water of infected 

 districts. This applies particularly to grazing sheep and 

 cattle, especially if feeding on low, wet pastures subject to 

 overflow. Certain fields, notably those in which the carcasses 

 of anthrax animals have lain or were buried (shallow graves), 

 or contaminated with the droppings or blood of patients 

 sufPering from the disease, are especially dangerous in this 

 regard. It is probable that healthy animals may carry spores 

 in the digestive contents without becoming infected them- 

 selves, their droppings, however, polluting the soil, drinking 

 water, and forage, thus infecting other less resistant animals. 

 The blood of the living or dead anthrax animal is also infec- 

 tive. Soil and water can be contaminated by the ofFal of 

 tanneries, hair- or rag-sorting establishments. Flesh-eating 

 animals can infect themselves by eating meat or blood con- 

 taining anthrax spores. In this way dogs and swine take the 

 disease. As fresh meat and blood usually contain only bacilli, 

 which are destroyed by the digestive juices, it is not as 

 dangerous as when stale. However, if very large quantities 

 are eaten, infection may follow, some of the bacilli escaping 

 the destructive influences of the gastric fluids. In swine the 

 crypts of the tonsils may serve as points of attack for the 

 spores taken in with the food and water. Milk does not 

 usually contain either spores or bacilli, but at times, especially 

 when the milk is bloody, they may be present. 



(6) Respiratory Tract. — The inhalation of dried spores from 

 contaminated dust, wool, hair, or rags is a common mode 

 of infection in man. While this is also probable in animals, 

 no proof is available. 



(c) Skin. — An infection through the intact skin is not prob- 

 able. When the skin is wounded, however, it may follow. 



The enzootics of a"nthrax among horses and mules in the 

 lower Mississippi Valley are said to be induced through 

 skin infection brought about by blood-sucking insects. 

 Recent experiments made by Morris of the Louisiana Agri- 

 cultural Experiment Station seem to prove that the horn fly 

 (Hsematobia irritans), the horse fly (Tabanus sp.), and 



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