BACTERIACE^:: THE SPOROGENIC AEROBES 273 



however, either because of lowered virulence of the germ or of 

 increased resistance of the host, and in these cases the bacteria 

 may be very scarce and difficult to find microscopically, even 

 after death of the animal. Cultures from the spleen will usually 

 show the presence of the bacillus there. The mechanism by 

 which the bacillus causes death is unknown. In the acute cases, 

 as in the mouse, the bacilli are so abundant in the blood that 

 mechanical interference with the circulation seems a plausible 

 explanation, but this certainly does not suffice for other types of 

 the disease in which chemical poisoning must play the chief 

 role. So far it has not been possible to demonstrate any powerful 

 poisons in cultures of the anthrax bacillus. It is probable that 

 the essential poisons are produced by a reaction between the 

 substance of the bacillus and the fluids of the host, particularly 

 the enzymes of the latter, which cause disintegration of the bac- 

 terial bodies. 



The infection is acquired by grazing animals through the 

 alimentary tract primarily, but also to some extent by inoculation 

 (contact, flies, intermediate objects). In man there are three 

 recognized types (a) malignant pustule, (b) pulmonary anthrax, 

 and (c) intestinal anthrax. Malignant pustule results from in- 

 oculation of the skin, especially in those who handle hides or care 

 for anthrax animals. It is at first a local pustular and necrotic 

 lesion tending to involve contiguous tissue by extension, but soon 

 invading the lymph vessels and walls of the veins. The bacteria 

 thus gain the blood stream and a rapidly fatal general bacteremia 

 supervenes. Recovery sometimes occurs before the disease be- 

 comes generalized. Pulmonary anthrax is caused by inhalation 

 of anthrax spores (woolsorter's disease). Intestinal anthrax 

 is uncommon in man but has occurred. Both are very fatal 

 forms of the disease. 



Immunity to anthrax was first successfully produced by Pas- 

 teur through vaccination with attenuated living cultures. Broth 

 cultures inoculated with bacilli taken directly from the animal 

 body were grown at 42C to 43C. At this temperature spores 



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