TUBERCULOSIS. 409 



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 

 ended June 30, 1911, 76,4:-i:S 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 as the unit of comparison the 

 number of cases of animals of a year and under aifected with tuber- 

 culosis, animals from 1 to 3 years old furnish 10 times, those 3 to 6 

 years old 30 times, and those more than 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 0.11 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 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 tlirough 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 liacillus which causes the disease is for the 

 same reason known technically as the Bacillus tuberculosis. 



There are undoubtedly ]iredisposing conditions which contribute 

 toward the development of the disease; some of these are found in 

 the animal body and others in the environment. An enfeebled condi- 

 tion caused by insufficient feed, exposure to great extremes of atmos- 

 pheric temperature and insanitary surroundings, or the drain occa- 

 sioned by heavy production of milk, appear to aid the development 



