CHAPTER V. 



CHRONIC INFECTIOUS DISEASES. 



TUBERCULOSIS. CONSUMPTION. 



Definition. — Tuberculosis is a chronic, contagio-infectious 

 disease due to the Bacillus tuberculosis and characterized by 

 the formation in the different organs of the body, of small 

 nodules, nodes, or larger irregular areas which tend to case- 

 ate, undergo fibroid degeneration, or calcify. 



Occurrence. — Tuberculosis occurs in all domesticated ani- 

 mals, although it is very rare in sheep. In fact all warm- 

 blooded animals and many cold-blooded ones (fish) are sus- 

 ceptible to it. In man one-seventh of the race die of it 

 (150,000 annually in the United States alone)., In animals 

 cattle, swine, and fowls are most commonly infected. The 

 prevalency of bovine tuberculosis, as in other contagious dis- 

 eases, depends upon the opportunity for infection and spread. 

 It is therefore most common in large herds confined in 

 stables and less frequent in small herds living in the open. 

 In the western ranges of the United States and in the great 

 open grazing districts of other countries (steppes of Russia, 

 South American pampas) tuberculosis is comparatively rare. 

 On the other hand, in the more densely populated parts of this 

 country (Atlantic seaboard, Middle West, neighborhood of 

 large cities) it is very prevalent. In practice a greater per- 

 centage of tuberculosis will be found in dairies and in herds 

 of full-blood cattle maintained and sold for breeding pur- 

 poses ("stud or seed cattle")- In both instances the oppor- 

 tunity for infection is great (indiscriminate purchase of new, 

 non-tuberculin-tested animals) and the close contact in which 

 cattle of these classes are kept still further favors the spread of 

 this contagion. While every State in the Union is infected, t 

 in some districts it is much less common than in others, and 

 even in badly infected districts whole herds of cattle are found 



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