THE CONTROL OF TUBERCULOSIS 147 



the water down through a common manger is an almost certain 

 way of passing on the disease to animals drinking the water after 

 an infected one. 



The disease may be brought into a herd by the purchase of 

 infected animals. The feeding of unpasteurized skim milk and 

 whey from creameries and cheese factories to calves and pigs 

 frequently brings in the disease. If these products are properly 

 pasteurized they are safe to feed. A healthy herd may become 

 infected through mingling with diseased animals at the fairs or by 

 occupying premises previously occupied by infected animals and 

 not disinfected. Similarly, infection may result from shipment 

 in contaminated cars. 



226. Physical symptoms not marked. — It has been men- 

 tioned that a cow may have the disease for years before physical 

 sjrmptoms are evident. In the advanced stage there may be 

 coughing and sometimes there is lameness due to the joints being 

 affected. The cow generally has a dull eye, a rough coat, a droop- 

 ing head and shows loss of weight. But these symptoms are not 

 satisfactory for detecting the disease. By the time they have 

 become evident the animal may have spread the disease through- 

 out the herd, as well as having been a liability for some time as 

 regards production. 



227. The tuberculin test. — Fortunately we have in the tuber- 

 culin test a method which will detect tuberculosis in its earliest 

 stages. The method is not perfect but it certainly has proved so 

 valuable that a man is foolish to disregard it. 



228. Control and eradication. — The first step for the inter- 

 ested dairyman is to find out whether he has any diseased animals 

 in his herd. This is done through the tuberculin test. An animal 

 which is shown to have the disease by this test is called a reactor. 

 Where reactors are found they must be removed from the herd. 

 Next the barn must be thoroughly disinfected to get rid of germs 

 present. Finally the herd must be so handled as to prevent future 

 contamination. This is an outline of the method of getting rid of 

 tuberculosis. The details will be brought out by a discussion of 

 the accredited herd plan. 



