438 DISEASES OF CATTLE. 



diseased before tubercle bacilli can appear in the milk. Experi- 

 ments made 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 the milk of such cows. 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 rec- 

 ognizable simply casts suspicion 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. AVhen we consider therefore the extent of tuber- 

 culosis and the hidden character of the disease, a certain amount of 

 suspicion rests upon all milk. Fortunately tubercle bacilli are read- 

 ily destroyed by the temperature 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 

 l)etter means of diagnosis are at hand it is incumbent upon all com- 

 munitias to have dairy cows examined or inspected, at least to the 

 extent of finding out whether the udder shows any signs of disease. 

 If this is detected, the affected 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 might 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 w^ith such virus. It was the 

 experiments and comparative studies of Theobald Smith, however, 

 which attracted special attention to the difference in virulence shown 

 by tubercle bacilli from human and bovine sources when inoculated 

 upon cattle. Smith mentioned also certain morphological and cul- 

 tural 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 dis- 

 ease in the human subject, but said : 



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

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

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

 conditions exist. 



