430 DISEASES OF CATTLE. 



with the milk of tuberculous cows in which there were no indications 

 of udder disease do not bear out this theory, since tubercle bacilli 

 have been found in their milk. Some authorities still believe that 

 the udder is diseased when the milk is infected, but that the disease 

 escapes observation. However this may be, the fact that the udder 

 may be diseased and the disease not recognizable simply casts sus- 

 picion upon all milk from tuberculous animals. We know that the 

 milk of tuberculous cattle may or may not contain tubercle bacilli 

 when the udder is apparently free from disease, but we have no rapid 

 method of determining whether in any given case the milk contains 

 tubercle bacilli or not. Moreover, the bacilli may be absent at one 

 time and present at another in milk from the same cow. When we 

 consider, therefore, the extent of tuberculosis and the hidden charac- 

 ter of the disease, a certain degree of suspicion rests upon all milk. 

 Fortunately, tubercle bacilli are readily destroyed by the tempera- 

 ture of boiling water, and hence both meat and milk are made entirely 

 safe, the former by the various processes of cooking, the latter by 

 boiling for a few moments. Until better means of diagnosis are at 

 hand it is incumbent upon all communities to have dairy cows exam- 

 ined or inspected, at least to the extent of finding out whether the 

 udder shows any signs of disease. If this is detected, the aiffected 

 animal should be killed at once or else all opportunity for the sale of 

 such milk removed by appropriate measures. The dangers from 

 infected milk may by these means be very materially lessened. 



Recently there has been much discussion of the question as to 

 whether human and animal tuberculosis are identical diseases and 

 as to the possibility of the tuberculosis of animals being transmitted 

 to man or that of man being transmitted to animals. 



The fact that tuberculous material from human subjects often 

 failed to produce serious disease in cattle was observed by a number 

 of the earlier investigators who experimented with such virus. It 

 was the experiments and comparative studies of Theobald Smith, 

 however, which attracted special attention to the difference in viru- 

 lence shown by tubercle bacilli from human and bovine sources when 

 inoculated upon cattle. Smith mentioned also certain morphological 

 and cultural differences in bacilli from these two sources, and in the 

 location and histology of the lesions in cattle produced by such 

 bacilli. He did not conclude, however, that bovine bacilli could not 

 produce disease in the human subject, but said : 



It seems to me tliat, accepting the clinical evidence on hand, bovine tubercu- 

 losis may be transmitted to children when the body is overpowered by larjre 

 numbers of bacilli, as in udder tuberculosis, or when certain unknown favorable 

 conditions exist. 



Koch, however, in his address at the British Congress on Tubercu- 

 losis, went far bevond this and maintained that " human tubercu- 



