DISEASES OF THE HORSE. 529 



The specific virus of anthrax was first discovered b}' Davaine in 

 1851. He recognized in the blood of animals suffering from anthrax 

 microscopic bodies in the form of little rods. It was not, however, 

 till a quarter of a century later that Pasteur defined the exact nature 

 of the bacillus, the mode of its propagation, and its exact relationship 

 to anthrax as the sole cause of the disease. In the animal body the 

 bacilli have a tendency to accumulate in the spleen, liver, and else- 

 where, so that these organs are much more virulent than the muscles 

 or less vascular tissues. When eliminated from the animal in the 

 excretions, or when exposed to outside influences by the death of the 

 animal and the disintegration of the tissues, the body of the rod is 

 destroj^ed and the spores onl}^ remain. These spores, which may be 

 called the seeds of the bacilli, retain their vitality for a long period; 

 the}^ resist ordinary putrefaction; they are unchanged by moisture; 

 and they are not affected by moderate heat. If scattered with the 

 debris of a dead animal on the surface of the ground, the}^ ma^^ remain 

 around the roots of the grass in a pasture or ma}" be washed to the 

 nearest low-lying ground or marsh. If buried in the body of an ani- 

 mal dead from anthrax, they may be washed deep into the ground, and 

 in later jenvs (in one proven case 17 years) be brought to the surface 

 and infect other animals. They are frequentlj^ brought to the 'surface 

 of the earth, having been swallowed b}" earthworms, in the bodies of 

 which they have been found. 



This accounts for the outbreaks at the time of the first rains after a 

 dr}^ season. During the latter the earthworm goes deep in the ground 

 in search of moisture; it finds the spore which has been washed there 

 in past years, swallows it, and afterwards brings it to the surface. 

 The virus is carried with the wool from infected sheep and remains in 

 it through the process of manufacture into cloth. The spores remain 

 in the hides of animals which have died of anthrax and retain their 

 vitality throughout months of soaking in the tanners' pits, the work- 

 ing of the harness maker or the cobbler, and after the oiling of the 

 completed leather. The dried spores in the dust from anj- of these 

 products may be carried by the atmosphere. 



Infection of an animal takes place througli inoculation or contact of 

 the bacillus or its spores with an abraded surface or mucous membrane 

 on a sound animal. In an infected district horses may eat the rich 

 pasturage of. spring and early summer with impunity, but when grass 

 becomes low they crop it close to the ground, pull up the roots around 

 which the virus may be lodged, and under these conditions the animals 

 are more apt to have abrasions of the lips or tongue by contact witii 

 dried stubble and the dirt on the roots, which favors the introduction 

 of the germs into the system. The virus may be introduced with food 

 and enter the blood-vessel S3^stem from the stomach and intestines. If 

 contained in the dust, dried hay, or on the parched pasture of late 

 14384—03 34 



