BOVINE TUBERCULOSIS. 65 



whose attitude is conservative and critical. In 1908 he stated : 



and it has been found that perhaps half of certain kinds of 

 tuberculosis in children, such as those of the glands of the 

 neck and abdomen, are due to infection from milk." (50) 



Insufficient work has been done to determine the percentage 

 of human tuberculosis caused by bovine tuberculosis. The Brit- 

 ish Royal Commission found the bovine type 14 times in 60 

 cases of human tuberculosis investigated by it (5). The sig- 

 nificant fact is that here is indisputable evidence to satisfy the 

 most conservative that tuberculosis is transmitted from cattle 

 to man. 



Intermediate types of tubercle bacilli. Some observers believe 

 that the study of a series of tubercle cultures reveals interme- 

 diate types varying from the extremes exhibited by human 

 and bovine cultures (3, 7, 20, 43). These intermediate-shave 

 been observed in both cattle and man. The observation has led 

 to the conclusion that certain characters of the tubercle organ- 

 isms are exceedingly variable. For instance, a bovine strain 

 in a child might after a time be modified by environment so 

 much as to disguise its original source. If this point of view 

 is taken, bacteriological distinctions — the only ones — between 

 tuberculosis in cattle and man break down, and the importance 

 conceded to bovine tuberculosis in connection with the public 

 health is consequently increased. 



Channels of infection. Alimentary infection was formerl>- 

 thought to give rise necessarily to primary tuberculosis in the 

 mesenteric lymph nodes. The rare occurrence of this con- 

 dition was used by Koch as an argument to prove that tuber- 

 culosis in children does not frequently originate from milk. 

 Experimental work with reference to this point has shown that 

 the primary lesion in animals need not necessarily occur in a 

 mesenteric lymph node. Tubercle bacilli from the intestinal 

 tract may travel to the lungs via lymph node, thoracic duct 

 and blood, causing the primary lesion in the capillaries of the 

 lung or elsewhere (30). It is also believed that infection 

 may enter through the tonsils and cause tubercular involve- 

 ment of organs anterior to the diaphragm without ever travers- 

 ing the abdominal organs. There is a growing belief based on 



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