BACILLUS TUBERCULOSIS. 129 



have spread the disease. This, however, is not thoroughly 

 proved, and recently the eminent Koch has asserted that this 

 mode of contamination is exceedingly rare, and is an equation 

 which in the treatment and the prevention of tuberculosis 

 may be altogether neglected. 



It has been assumed that human, avian, and bovine tuber- 

 culosis are identical. In a remarkable paper on tuberculosis 

 by Koch, read before the Tuberculosis Congress in 1901, at 

 Berlin, he denies this identity, and shows by a number of 

 experiments that cattle cannot be inoculated with the secre- 

 tion of tuberculous patients, and that man is not affected by 

 eating meat from contaminated oxen. 



It must not be overlooked, however it may shock the aes- 

 thetic senses of some people, that tubercle bacilli of the human 

 type may be swallowed, either in contaminated fluids, food, or 

 dust, and infection from these sources in this manner does not 

 conflict with any one's opinion, and must be reckoned with 

 most seriously. 



As regards the transmission of tuberculosis, the part played 

 by heredity is almost nil. It has failed of demonstration 

 that foetuses or young children from intensely tuberculous 

 mothers have in their secretions or tissues the tubercle bacil- 

 lus ; and reasoning by analogy, as in Bang's method, the sepa- 

 ration of newborn calves from their tuberculous mothers has 

 completely succeeded in eliminating tuberculous diseases 

 from these calves, it must be assumed that like precautions 

 would produce identical results in man. 



The tubercle bacilli secrete a poisonous material, which is 

 chiefly contained in the bacterial cells themselves, and is 

 known by the name of tuberculin. This tuberculin is believed 

 to be a preventative against tubercular diseases ; and in 1890 

 Koch proclaimed that by means of injections of this substance 

 he had succeeded in curing tuberculosis. This promise has not 

 been fully realized, but Koch's discovery has given us valu- 

 able information, and has demonstrated that by injection of 

 this tuberculin healthy animals may be recognized and so 

 separated from tuberculous ones long before the disease could 

 be diagnosed in the latter by physical signs ; for the former 

 9 M. B. 



