ANTHRAX. 449 



Cause. — The cause of anthrax is a microscopic organism known as 

 the anthrax bacilhis. (See PL XXVIII, fig. 7.) In form it is 

 cylindrical or rodlike, measuring ^-^ to -z-sTnr inch in length and 

 •JTDTTo inch in diameter. Like all bacteria, these rodlike bodies 

 have the power of indefinite multiplication, and in the bodies of 

 infected animals they produce death by rapidly increasing in num- 

 bers and producing substances which poison the body. In the blood 

 they multiply in number l_iy becoming elongated and then dividing 

 into two, each new organism continuing the same process indefinitely. 

 Outside the body, however, they multiply in a different way when 

 under conditions unfavorable to growth. Oval bodies, which are 

 called spores, appear within the rods, and remain alive and capable 

 of germination after years of drying. They also resist heat to a 

 remarkable degree, so that boiling water is necessary to destroy them. 

 The bacilli themselves, on the other hand, show only very little re- 

 sistance to heat and drj'ing. It has long been known that the anthrax 

 virus thrives best under certain conditions of the soil and on terri- 

 tories subject to floods and inundations. The particular kinds of 

 soil upon which the disease is observed are black, loose, warm, humous 

 soils; also those containing lime, marl, and clay, finally peaty, swampy 

 soils resting upon strata which hold the water, or, in other words, are 

 impervious. Hence fields containing stagnant pools may be the source 

 of infection. The infection may be limited to certain farms, or even 

 to restricted areas on such farms. Even in the Alps, more than 3,000 

 feet above sea level, where such conditions prevail in secluded valleys, 

 anthrax persists among herds. 



Aside from these limitations to specific conditions of the soil, 

 anthrax is a disease of world-wide distribution. It exists in most 

 countries of Europe, in Asia, Africa, Australia, and in our own 

 country in the lower Mississippi Valley, the Gulf States, and in some 

 of the Eastern and Western States. It seems to be gradually spread- 

 ing in this country and every year occurs in new districts. 



Meteorological conditions also have an important share in deter- 

 mining the severity of the disease. On those tracts subject to inun- 

 dations in spring a very hot, dry summer is liable to cause a severe 

 outbreak. The relation which the bacillus bears to these conditions 

 is not positi\'ely known. It may be that during and immediately 

 after inundations or in stagnant water the bacilli find nourishment 

 enough in the water here and there to multiply and produce an 

 abundant crop of spores, which are subsequently carried, in a dry 

 condition, by the winds during the period of drought and dissemi- 

 nated over the vegetation. Animals feeding upon this vegetation 

 may contract the disease if the spores germinate in the body. 



Another source of the virus, and one regarded by many authorities 

 as perhaps the most important, is the body of an animal which has 

 33071°— le 29 



