INFECTIOUS DISEASES. 541 
lands dry out during the heat of simmer and ave then covered with 
light rains. Decaying vegetable matter seems most favorable for 
nourishing and preserving the virus. 
The direct cause of anthrax is always infection of a previously 
sound animal, either directly from a diseased animal or through 
various media which contain excretions or the débris from the body 
of one previously infected. 
The specific virus of anthrax was first discovered by Davaine in 
1851. He recognized microscopic bodies in the form of little rods in 
the blood of animals suffering from anthrax. It was not, however, 
till a quarter of a century later that Pasteur defined the exact nature 
of the bacillus, the mode’of its propagatjon, 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 
cr 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 
destroyed and the spores only remain. These spores, which may be 
called the seeds of the bacilli, retain their vitality for a long period; 
they resist ordinary putrefaction; they are unchanged by moisture; 
and they are not affected by moderate heat. If scattered with the 
débris of a dead animal on the surface of the ground, they may re- 
main around the roots of the grass in a pasture or may bé washed to 
the nearest low-lying ground or marsh. If buried in the body of an 
animal dead from anthrax, they may be washed deep into the ground, 
and in later years (in one proved case 17 years) be brought to the 
surface and infect other animals. They are fréquently brought to 
the surface of the earth, having been swallowed by earthworms, in 
the bodies of which they have been found. 
This accounts for the outbreaks at the time of the first rains after a 
dry 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 any of these 
products may be carried by the atmosphere. 
Infection of an animal takes place through inoculation or contact 
of the bacillus or its spores with an abraded surface or mucous mem- 
brane, on a sound animal. In an infected district horses may eat with 
impunity the rich pasturage of spring and early summer, but when 
