TUBERCULOSIS. Ill 



insisted that the two bacteria were different from each other, 

 and so decidedly different that there was little likelihood 

 of the disease being carried from man to cattle or from 

 cattle to man. The experiments that followed Professor 

 Koch's paper have in a measure borne out his conclusions, 

 but not the inferences which he drew from them. It is at 

 the present time recognized that there are differences between 

 the bacilli derived from mankind and from cattle. The differ- 

 ences show themselves in a number of points, both in their 

 method of growth in laboratory experiments and in their 

 power of producing disease. For experimental animals the 

 bovine bacillus proves to be more virulent than the human 

 bacillus. Experiments upon mankind have not as yet been 

 definite enough to determine whether or not this holds good 

 in regard to the bovine bacillus when inoculated into man. 

 But while these two types of bacilli are recognized to-day as 

 showing variations, it is generally . believed that this indi- 

 cates that they are not different species of organisms, but 

 merely varieties of the same one produced by the different 

 conditions under which they live. The bacillus growing in 

 the body of the bovine animal develops slightly different 

 characteristics from the organisms developing in man, and 

 these differences are generally looked upon to-day as simply 

 variations in the characters of the same organism, the two 

 types being regarded as essentially identical. If this con- 

 clusion is correct it would follow that the inference drawn 

 by Professor Koch, that the disease cannot pass from cattle 

 to man or from man to cattle, is incorrect. Indeed, it is 

 positively proved that the human bacillus can produce tuber- 

 culosis in cattle, though commonly of a mild character. 



3. It has been demonstrated beyond peradventure that if 

 a tuberculosis infection is located in the mammary gland of 

 a cow, the milk of the animal is quite sure to be infected 

 with the tubercle bacillus. The location of tuberculosis 

 in the udder is not very common but it does occur in a small 



