TUBERCULOSIS 43 



other hand, this animal succumbs in most instances in about three 

 weeks to the bovine variety. Intravenous, intraperitoneal, intraocular 

 and subcutaneous inoculations result in generalized fatal tuberculosis. 



Cattle, which as we have seen are highly resistant to the human 

 variety, succumb readily to the bovine, whatever the method of inocu- 

 lation. Calves fed on pure cultures or on the milk of tuberculous 

 cows speedily develop the disease, which usually begins in the forma- 

 tion of ulcers in the upper intestine and extends to the mesenteric, 

 lymphatic and retropharyngeal glands. Infection may result from a 

 single feeding. Calves from tuberculous cows are free from infection, 

 but one nursing from the mother may infect. The inhalation of a 

 very minute portion (0.01 mg.) of a pure culture is followed by the 

 development of pulmonary tuberculosis. 



Sheep, hogs and goats are highly susceptible to the bovine variety, 

 much less so to the human. 



It seems safe to say that tuberculosis among our domestic animals 

 results generally from infection with the bovine rather than the human 

 variety. However, some facts need to be stated. Tuberculosis is 

 common among chickens and it is quite natural to suppose that these 

 animals become infected by picking up human or bovine material, but 

 experiments show that chickens are immune to both these varieties. 

 Feeding, intravenous and subcutaneous inoculations of these varieties 

 do not develop tuberculosis in chickens. The bacilli retain their vital- 

 ity in these fowls for a long time but fail to develop tuberculosis in 

 the hosts, as has been demonstrated by inoculation of susceptible 

 animals, such as the guinea-pig. Apes seem to be equally susceptible 

 to the human and bovine varieties. 



Having ascertained that our domestic animals do not run great 

 risk in being infected with the human variety, let us see what danger 

 there is to man from infection with the bovine variety. Is it wise to 

 follow the advice of Koch and neglect milk as a factor in the causation 

 of tuberculosis in man ? This important question has been investigated 

 in this country by Park and Krumwiede, by an English commission, 

 by two German commissions, and by many individuals in various parts 

 of the world. In 1,441 deaths from tuberculosis in man, the variety 

 of the bacillus has been determined. In 117 of these (8.1 per cent.) 

 the bovine variety alone has been found. In seven cases (0.5 per 



