TUBEECULOSIS. 411 



Keports of tuberculin tests made on 400,000 cattle in the United 

 States during the years 1893 to 1908 by Federal, State, and other 

 officers with tuberculin prepared by the Bureau of Animal Industry 

 show 37,008 reactions, or 9.25 per cent. These were mostly dairy 

 cattle, and in some cases herds were suspected of being diseased. 



Later reports of tuberculin tests made in the United States from 

 July 1, 1917, to March 1, 1922, on 3,911,546 cattle by State, county, 

 and Federal officers engaged in cooperative tuberculosis eradication 

 work showed 153,046 reactions, or 3.9 per cent. 



All cattle in the District of Columbia, numbering 1,701, were tested 

 with tuberculin in 1909-10, and 18.87 per cent reacted. In 1909-11 

 herds in Maryland and Virginia supplying milk to the District of 

 Columbia were tested, with 19.03 and 15.38 per cent of reactions, 

 respectively, among 4,501 cattle. 



All cattle in the District of Columbia were tuberculin tested in 

 1920-21, numbering 1,313, and 5 animals reacted, or 0.4 per cent, 

 demonstrating that tuberculosis may be eradicated from all the herds 

 in a circumscribed area. 



The beef cattle of the United States show a much smaller propor- 

 tion of the disease than dairy cattle, though the percentage of cattle 

 found tuberculous in the GoA^ernment meat-inspection service has 

 increased considerably in recent years. This increase is due partly, 

 but not wholly, to more stringent inspection. Of 7,781,030 adult 

 cattle slaughtered under Federal inspection during the fiscal year 

 ended June 30, 1911, 76,448 were found tuberculous, a percentage 

 of 0.98. 



From the statistics above referred to, and other data, it appears 

 that in the more densely populated areas of Europe and America 

 from 5 to 50 per cent of the dairy cattle are more or less affected with 

 tnberculosis, while the proportion of beef cattle affected is distinctly 

 less, ranging from 0.14 to 30 per cent. This difference is due to a 

 number of causes. Beef cattle average younger when slaughtered. 

 They are not so frequently stabled, and are for that reason less liable 

 to infection, and as the males constitute a large proportion of this 

 class of animals the effect of milk secretion in lowering the vital 

 forces is not so apparent. In the United States it has been estimated 

 that about 10 per cent of the dairy cattle are tuberculous, while only 

 about 2 per cent of the beef cattle are so infected. 



Cause and nature of the disease. — The cause of tuberculosis is the 

 tubercle bacillus, which gains entrance to the body, lodges somewhere 

 in the tissues, and begins to grow and multiply at that point. As this 

 bacillus vegetates and increases in numbers it excretes substanceis 

 which act as irritants and poisons and which lead to the formation of 

 a small nodule, called a tubercle, at the point of irritation. As the 

 bacilli are disseminated through the animal body they affect many 

 parts and cause the formation of an enormous number of tubercles. 

 By the union of such tubercles, masses of tubercular material are 

 formed, which in some cases are of great size. The disease is called 



