MICROBIAL DISEASES OF MAN AND ANIMALS. 6oi 



ends are slightly rounded, but those in contact are quite square, and slightly larger in 

 diameter than the middle of the cell. Involution forms are obtained by culture on 

 potato or at temperatures of 40 to 42. It forms oval spores without distortion 

 of the mother cell (Fig. 102). Free oxygen is necessary for the development of these 

 bodies, and a temperature between 18 and 41. Spore germination is polar. By 

 culture at 42 an asporogenous variety is formed. It stains readily with the aniline 

 dyes and also by Gram's method. Under certain conditions a capsule may be seen. 

 The organism is aerobic, in the body it grows as a facultative anaerobe. Its optimum 

 temperature is 37, minimum 12, maximum 45. It forms characteristic wavy and 

 filamentous colonies on gelatin and agar, it liquefies gelatin, produces an arborescent 

 growth in gelatin stab cultures, coagulates and peptonizes milk with an alkaline 

 reaction. Thermal death-point of the spores in liquids is four minutes at 100, in hot 

 air 140 for three hours. Mercuric chloride, 1:1000, destroys the spores in a few 

 minutes, and 4 per cent carbolic acid with hydrochloric acid 2 per cent in one hour. 



Zoologically, anthrax is the most widespread of infectious diseases; 

 white mice, guinea-pigs, rabbits, sheep, cattle, horses and man are sus- 

 ceptible. Old rats are insusceptible. Von Behring, Metchnikoff and 

 others have shown that the serum of white rats contains a lysin capable 

 of dissolving the bacterium in vitro. Pigs are occasionally infected; the 

 carnivora generally are refractory, the bear and cat being less resistant. 

 Most birds are insusceptible, but some small birds, like the sparrow, are 

 more susceptible. Cold-blooded animals are refractory. 



Infection occurs: Through the food, giving rise to intestinal anthrax. 

 Cattle and sheep are usually infected in this manner by spores, the bac- 

 terium being destroyed by the gastric juice. In man infection through 

 food rarely occurs. 



Through the air. Infection by inhalation through the lungs occurs 

 in man through the medium of dust contaminated by anthrax spores, 

 hence the name " wool-sorter's disease." 



Through wounds. This method usually occurs in man and also in 

 sheep. Cutaneous infection comes through a scratch or wound, and 

 gives rise to a carbuncle hence the name " malignant pustule." It 

 occurs most frequently among employees of tanneries, wool-sorters, 

 veterinary surgeons, and those whose occupation brings them into touch 

 with infected animals, their hides or products. 



The incubation period is a short one, even in the naturally occurring 

 disease; inoculated laboratory animals die in twenty-four to forty-eight 

 hours. The bacteria appear in the blood about fifteen hours after inocu- 

 lation, and at death the blood simply swarms with the organism. The 

 veins are turgid, and the blood is often very dark, and coagulates slowly. 



