Disease Bacteria in Milk. 77 



Putrefaction and decomposition even, will not quickly 

 destroy its vitality. Direct sunlight is, however, an effi- 

 cient disinfecting agent, and, even in diffused light the 

 bacilli are destroyed in a few days. 



75. Prevalence among* cattle. Tuberculosis not 

 infrequently affects many species of warm-blooded ani- 

 mals, but it is particularly prevalent among cattle in cer- 

 tain regions of the world. 



The recent introduction of the tuberculin of Koch as 

 an aid in the diagnosis of the disease in cattle has shown 

 the trouble to be more widely spread than was at first 

 believed, but sufficient data have not yet been collated 

 to enable an accurate estimate to be made. 



In Denmark the percentage of affected animals has 

 been shown by Bang to be very high, ranging from 

 30-40% . Concerning the distribution of the disease in this 

 country, data is still very meager. In 15,000 head tested 

 under the auspices of the U. S. Dept. of Agriculture, 

 19% showed a reaction. Unquestionably it is more 

 widely disseminated, and a larger percentage of stock are 

 affected in the older dairy regions of the east than in the 

 west. The amount of disease among the range stock of 

 the western plains is relatively small. 



76. Tuberculin test. The tuberculin test is made by 

 injecting into the animal a small quantity of a liquid 

 known as tuberculin, which is a sterile glycerine extract 

 of the growth products of the tubercle bacillus. The re- 

 sults obtained by the use of this test show that it is far 

 superior to the physical methods of examination, it being 

 possible to detect the disease in its earliest stages. When 

 tuberculin is inoculated into an animal it causes a febrile 

 reaction in those cases affected with this disease; the 

 rise in temperature usually exceeding the average normal 



