418 DISEASES OF CATTLE. 



Eeports 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. 



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. 



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 Government 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 end- 

 ing June 30, 1911, 76,448 were found tuberculous, a percentage of 0.98. 



It has been observed that tuberculosis increases in frequency with 

 the age of the animals. If we take the number of cases of animals of 

 a year and under affected with tuberculosis as the unit of comparison, 

 animals fi'om 1 to 3 years old furnish 10 times, those 3 to G years old 

 30 times, and those over 6 years 40 times the number of cases. 



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 

 tuberculosis, 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. 



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 substances 

 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 

 points 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 

 tuberculosis because it is characterized by the formation of these 

 peculiar nodules, and the bacillus which causes the disease is for the 

 same reason known technically as the Bacilhis tuhercidosis. 



