228 MICROBIOLOGY 



The mode of action of Bacterium anthracis is as yet not 

 clearly determined. It has been asserted that death is brought 

 about to a large extent by purely mechanical means, such as 

 capillary obstruction. A true extracellular toxin or endotoxin 

 has not been demonstrated for the anthrax bacterium. It is a' 

 matter of record that neither culture nitrates nor dead bacteria 

 have any noticeable toxic effect upon test animals, and they do 

 not exert an appreciable immunizing action. 



*. Spontaneous infection of animals takes place largely by 

 way of the alimentary canal, the bacteria being taken in with 

 the food. The bacteria are swallowed as spores, and therefore 

 resist the acid gastric juice. In the intestines they develop 

 into the vegetative form, multiply, and gradually invade the 

 system. The large majority of cattle infections are of this 

 type. Direct subcutaneous infection may also occur spon- 

 taneously when small punctures and abrasions about the mouth 

 are made by the sharp spicules of the hay, straw, or other va- 

 rieties of fodder. 



Infection by inhalation is probably rare among animals. 

 Transmission among animals is usually by the agency of the 

 excreta or unburned carcasses of infected animals. The bac- 

 teria escaping from the body are deposited upon the earth, 

 which forms a suitable place for sporulation. The spores may 

 then remain in the immediate vicinity, or may be scattered by 

 rain and wind over a considerable area. The danger from 

 buried carcasses, at first suspected by Pasteur, is probably 

 very slight owing to the fact that the bacteria can not sporu- 

 late in the anaerobic environment to which the burying- 

 process subjects them. The disease in cattle and sheep is 

 usually acute, death following within one or two days. The 

 mortality is extremely high. 



In man the disease is usually acquired by cutaneous in- 

 oculation or by inhalation and through the alimentary tract. 

 M'Fadyean 10 found anthrax bacteria in the milk that had 



10 M'Fadyean. Jour, of Comp. Path, and Therap., Vol. XXII 

 (1909) p. 148. 



