WHY THERE IS A MILK PROBLEM 25 



estimated that perhaps seven per cent of the tubercu- 

 losis in man is of bovine origin." The basis of this 

 estimate does not appear; in view of the others it looks 

 very liberal. 



Altogether, while it seems to be impossible to state 

 at present the exact amount of human tuberculosis of 

 bovine origin, it is to be concluded that tuberculous 

 milk, though not the overwhelming menace it is some- 

 times thought to be, is a distinct factor in the milk 

 problem. 



Tubercle bacilli may be detected in market milk. 

 Evidence from four typical American cities (Chicago, 

 New York, Washington, Rochester, N. Y.), summed 

 up by Rosenau, 14 shows that out of a total of 551 

 samples examined the bacilli were found in 46, or 8.3 

 per cent. This figure is doubtless an underestimate, 

 for the laboratory methods may fail to detect the bacilli 

 when present only in small numbers. At Roches- 

 ter, N. Y., 12.65 per cent of milk samples taken from 

 185 retailers reacted to animal tests for tuberculosis. 15 

 Unfortunately such tests give no indication of the 

 numbers of tubercle bacilli in the samples. 



Tuberculous cows infect the milk through tubercu- 

 lous udders, but more largely through the manure, in 

 which the bacilli are excreted in great numbers and 

 which gains access to the milk at milking time. The 

 infection is derived not only from obviously tuber- 

 culous cows but also from many which show no phys- 

 ical signs of the disease and whose condition can be 

 determined only by the tuberculin test, to which fur- 

 ther reference will be made in a later chapter. 



