100 THE MODERN MILK PROBLEM 



tests be shown "good," and low-bacteria milks "bad." 

 This may readily be understood, for the bacterial flora 

 depends not merely upon the amount of dirt con- 

 tamination but also and much more largely upon 

 the kind of contamination, the age of the milk, and the 

 temperature at which it has been kept. Hence the 

 dirt tests can throw light on but one item in milk 

 sanitation viz., the amount of sediment in unstrained 

 milk (previous straining or clarification practically 

 destroying the value of the tests) and are far from 

 being a general criterion of the conditions of production 

 and handling. 



THE TUBERCULIN TEST 



One of the noteworthy discoveries of modern sani- 

 tary science is that bovine tuberculosis may be trans- 

 mitted to human beings through the medium of cow's 

 milk.* At the same time a test namely, the tuber- 

 culin test f has been perfected by which tuberculosis 

 can be determined in that important class of cows which 

 are infected yet show no physical symptoms. This 

 adds to veterinary examination an exceedingly valu- 

 able diagnostic agent. 



The tuberculin test appears to have been first re- 

 quired, in addition to physical examination, by the 



* This matter, with some reference to the amount of human tuber- 

 culosis of bovine origin, was touched upon in Chapter I. 



f The test consists essentially in the hypodermic injection of an 

 emulsion of killed bovine tubercle bacilli (tuberculin). Animals in- 

 fected with tuberculosis react by a marked rise in temperature. This 

 reaction has been accepted in the courts, as well as in veterinary medi- 

 cine, as a thoroughly reliable test of a very high degree of accuracy 

 when competently applied. 



