BLACKLEG (so named because the tumors affect the legs oftener than other parts of the body), BLACK QUARTER, or SYMPTOMATIC AN THRAX. An infectious disease due to the action of Bacterium ehanroli. It is confined almost en tirely to cattle, but eases have occurred also in sheep, goats, camels, pigs, and horses. Alan is immune to it. The disease is characterized clinically by the development of tumors in the muscles of various parts of the body, producing, when stroked, a crackling sound, which serves to distinguish this disease from anthrax. After death the tumors become infiltrated with blood and serum containing gas-bubbles; and this again distinguishes blackleg from anthrax, as the tumors of the latter are not found to contain any gas. Further, in blackleg the spleen is not af fected and the blood coagulates quickly, while in anthrax the spleen is much enlarged and the blood clots more slowly. Blackleg has long been known as a disease of cattle, but has, until within recent years, been generally confused with anthrax. The blackleg bacterium does not de velop in the presence of free oxygen. In the blood it is slightly motile. The symptoms of black leg are loss of appetite, debility, and great eleva tion of temperature. The disease runs its course very rapidly, and is fatal in nearly all cases. Cat tle between the ages of six and eighteen months are most susceptible, young calves and old ani mals being more resistant. Fat cattle seem to ne especially liable to infection. The symptoms appear suddenly within from one to three days after infection. The tumors may develop at once or may be preceded by the symptoms of fever and trembling. A lameness of the legs is usually observed, and is due to the muscular tumors which almost always accompany the dis ease. The animal manifests considerable pain, and falls to the ground soon after the develop ment of the first symptoms. The part which is
most affected becomes swollen and assumes a black or blue color, which is due to the infiltra tion and coagulation of blood within it. The dried spores of the blackleg bacterium may be carried in hay or other dry feed, and it is quite possible that animals may he infected by eating such material. Recent investigations, however, indicate that infection most frequently takes place through wounds of the skin, mouth, or tongue, such as would be produced by various spines and the awns of grasses.
Blackleg is found in nearly all countries of the globe. In the mountains of France it is known as mal de inontayne, in Denmark as rashsyge, and in Germany as Rauschbrand. In the United States it is most prevalent in Texas, Kansas, Nebraska, South Dakota. and Colorado.
Medical treatment of blackleg has been uni formly unsuccessful and is not to be recom mended. on the other hand, preventive vaccina tion has given very satisfactory results. Out of 500.000 cattle vaccinated in Europe, only one half of one per cent. subsequently died df black leg. Equally striking results have been obtained by the Bureau of Animal Industry of the United States Department of Agriculture. This bureau has perfected a method of producing immunity against blackleg by one vaccination, requiring less time than the old method, in which two inoculations were made, with an attenuated and strong vaccine. respectively. Stockmen may now buy the vaccine and inoculate their own cattle. For further study of blackleg. consult: A..1.Alur ray and others, "Special Report on Diseases of Cattle," Report of United A`4tatcs Department of Agriculture (Washington, 1892) ; Bureau of Ani mal Industry. 15th A 1177 nal Report, p. 27 Moeard and Leclainehe, Les maladies microbi ennes des animaux ( Paris, 1898).