460 " DISEASES OP CATTLE. 



causal standpoint. The disease is produced by a specific bacillus, 

 readily distinguishable from that causing anthrax. (PI. XXVIII, 

 fig. 4.) Cattle between 6 months and 2 years of age are the most 

 susceptible. Sucking calves under 6 montlis are rarely attacked, nor 

 are they so susceptible to inoculation as older animals. Cattle more 

 than 2 years of age may become affected, but such cases are infre- 

 quent. Sheep and goats may also contract the disease, but man, 

 horses, hogs, dogs, cats, and fowls appear to be ijnmune. 



Like anthrax, blackleg is more or less restricted to definite local- 

 ities. There are certain pastures upon Avhich the disease regularly 

 appears in the summer and fall of the year. As to any peculiarities 

 of the soil nothing is definitely known. Some authors are inclined 

 to regard moist, undrained, and swampy pastures favorable to this 

 disease, but these theories will hardly hold, as it is found in all kinds 

 of soil, in all altitudes, at all seasons of the year, and under various 

 climatic conditions. It occurs in this country from the Atlantic to 

 the Pacific and from Mexico to Canada, but it is more prevalent in 

 the Western and Southwestern States. In Europe it exists in France, 

 various parts of Germany, in Belgium, Norway, Denmark, Italy, 

 and in the Alps of Switzerland. In Africa it occurs in Algeria 

 and to some extent in Natal and bordering countries. In South 

 America it prevails quite extensively throughout Argentina. Cattle 

 in Cuba and Australia also suffer. 



Cause. — The cause of the disease is a bacillus resembling in some 

 minor respects the anthrax bacillus and differing but little from it 

 in size. It also possesses the power of forming within itself a spore. 

 In Plate XX^T^II, figure 4, this is represented as an uncolored spot 

 located in one end of the rod, which is enlarged so that the rod 

 itself appears more or less club-shaped. What has already been 

 stated concerning the significance of the spore of tlie anthrax bacillus 

 applies equally well to these bodies. They resist destructive agents 

 for a considerable time, and may still produce disease when inocu- 

 lated after several years of drying. This fact may account for the 

 occasional appearance of blackleg in stables. In order to meet the 

 requirements for the development of the spores, which takes place 

 only in the absence of the atmosphere, it is necessary that the wound 

 be very small and deep enough to penetrate the subcutaneous tissue. 



Several observers have found this organism in the mud of swamps. 

 By placing a little of the mud under the skin, the disease has been 

 produced. 



Since the disease may be produced by placing under the skin 

 material containing the specific bacilli and spores, it has been 

 assumed that cattle contract the disease through wounds, principally 

 of the skin, or very rarely of the mouth, tongue, and throat. Slight 

 wounds into which the virus may find access may be caused by 



