BOVINE TUBERCULOSIS. 61 



is afforded. It is the practice for dairymen supplying cream- 

 eries to take back skim-milk to feed to the calves. This skim- 

 milk is mixed indiscriminately at the creamery, and thus a 

 ready means for the dissemination of the disease from herd to 

 herd is afforded. The heating of skim-milk, whey, etc., at 

 the factories, to kill the tubercle bacilli before distribution to 

 the dairymen for feeding purposes, is an important measure 

 for restricting the spread of the disease. It has been made 

 com])ulsory in some states. 



Prevalence in herds. It is rarely that figures on the numl^er 

 of reacting animals in large herds supijlying market milk are 

 available ; for the conditions are so bad that owners are cautious. 

 From reliable sources, the writer has learned of herds of one to 

 two hundred cows showing 90% reacting. Averages including 

 results from small herds are lower. In New York State figures 

 compiled from results of testing under the supervision of the 

 Commissioner of Agriculture, and from tests by private i>rac- 

 titioners, show 32% of the cows reacting. The disease was 

 found in 61% of the herds tested (22). Recent tests of cows 

 supplying Washington, D. C, show 18.6% reacting. These 

 figures are lower than true conditions, for the cows tested 

 were either in herds where efforts to eradicate the disease 

 were in progress, or where the owner had no sus])icion of ser- 

 ious trouble. The writer encountered practicalh- the same 

 figures in Berkele>-, Cal., among herds where the owners did 

 not refuse permission to test. Among 1022 cows in 11 herds 

 in California, Dr. Haring and the writer have found 31.9'/- 

 reacting. Eighty-two per cent, of the herds were found to 

 contain infected animals. The figures are compiled only from 

 results of whole herds, tested for the first time. Of 71 cows 

 pastured on vacant lots in Berkelex', only 8'/r reacted (55). 

 These figures concerning the prevalence of tuberculosis among 

 cattle in California were derived from results oljtained largely 

 in herds in the San Francisco Ba\" region furnishing" city milk 

 sujiply. It is not permissible to generalize from them regard- 

 ing the prevalence of the disease among cattle elsewhere, in 

 herds managed differently. 



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