402 DISEASES OF CATTLE. 



but not wholly, to more stringent inspection. Of 7,116,275 adult 

 cattle slaughtered under federal inspection during the fiscal year end- 

 ing June 30, 1908, 68,395 were found tuberculous, a percentage of 0.96. 



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 com- 

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

 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 Bacillus tuberculosis. 



There are undoubtedly predisposing 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 

 condition due to insufficient food, exposure to great extremes of 

 atmospheric temperature and insanitary surroundings, or the drain 

 occasioned by heavy production of milk appears to aid the develop- 

 ment of the bacillus, and there is also a special individual suscepti- 

 bility in some cases which may be otherwise described as an inability 

 of the animal tissues to resist and destroy the bacilli when they have 

 penetrated to the inner recesses of the body. 



Among the conditions of environment which aid the development 

 of tuberculosis may be mentioned stabling with lack of ventilation, 

 damp buildings, the keeping of many animals together, drafts of air 

 which cause colds and catarrhs, and, in general, everything which 



