92 PRACTICAL DAIRY BACTERIOLOGY 



are capable of producing tuberculosis in man a question to be 

 noticed presently they will do so only when present in con- 

 siderable numbers. The human body has certain powers of 

 resistance against them, and the danger in swallowing a few 

 is comparatively small, whereas, if large numbers are taken 

 into the body the danger is greater. Hence, milk that con- 

 tains only a very small number of these germs, scattered 

 somewhat indefinitely, is practically harmless, and would prob- 

 ably never produce tuberculosis; whereas milk that contains 

 them in larger numbers, so that a person who takes a drink of 

 it would swallow considerable numbers of the germs, is more 

 likely to be a source of danger. 



The Use of Milk in Tuberculous Cattle. The possibility of the 

 distribution of tuberculosis by means of milk has a number of 

 very practical bearings upon dairying. Experiment has shown 

 that such milk is liable to produce tuberculosis when fed to 

 susceptible animals. The animals that most commonly acquire 

 the disease from milk are calves and pigs. The milk of tuber- 

 culous cows is, in many cases, the source of tuberculosis among 

 calves feeding upon the milk. Whether calves from tuberculous 

 mothers can be reared without danger of the disease is one that 

 not unfrequently arises as a practical question. It has been 

 demonstrated that, excepting in the very rarest of instances, 

 this disease is not hereditary, and that calves when born, even 

 though their mother is diseased, are free from it. Under these 

 circumstances, if they can be kept later from infection, they may 

 be raised with as good chances for health as any other calves. 

 In order to do this, however, they must not drink their mother's 

 milk, but must be removed from tuberculous mothers and fed 

 only upon the milk of healthy animals, or upon milk that has 

 been pasteurized. If this is done, there is no need of sacrificing 

 calves of mothers that are suffering from tuberculosis. 



There is little doubt, however, that by means of the milk 

 of such animals this disease has become common in our 



