DISEASES COMMUNICABLE IN MILK 



37 



As illustrative of the danger of this first mode, the data collected by 

 Russell are convincing; they appear in Table 17. 



TABLE. 17. THE RELATION BETWEEN UNSTERILIZED SKIM-MILK FROM CREAMERIES 

 AND BOVINE TUBERCULOSIS (RUSSELL) 



1 Group A comprises seven creameries immediately adjacent to Medina and Oak 

 Park. 



2 Group B comprises four creameries near but not contiguous to Medina and 

 Oak Park. 



The reacting animals in the herds of the Medina and Oak Park 

 creameries were nearly all raised on the farm and were fed skim-milk 

 returned in an unsterilized condition from the two creameries whereas 

 the reactors in groups A and B were mostly acquired by outside purchase. 



The buying in of tuberculosis has been very common in the past. 

 Some dairymen have been so blinded to aught but immediate gain, as to 

 purchase cows they knew were diseased, carrying them through a milking 

 period and thereafter sending them to the block; others unaware or un- 

 able to appreciate what they were doing have brought diseased animals 

 into their herds with the result that as the newcomers developed open 

 cases and became germ scatterers others succumbed. In truth, cows 

 with open cases are the most effective disseminators of the disease. Ex- 

 perience has proven that bovine tuberculosis is most prevalent in dis- 

 tricts supplying the city milk trade. Cows are pushed to the limit of 

 production and farmers feel that they must sell every drop of milk ; con- 

 sequently calves are not raised, so that replacements and additions to 

 the herds are made by purchase. This constant movement of cattle 

 from one herd to another has had the effect of spreading the disease more 

 rapidly than under the natural condition where the herd practically 

 maintained itself. 



The Diagnosis of Tuberculosis. The question arises, how it may be 

 determined whether or not a dairy animal has tuberculosis? Four 

 methods of diagnosis are in use, namely: (1) microscopical examination of 

 excised tissue which is obviously of limited application; (2) microscopical 

 and bacteriological examination of discharges of various sorts from the 

 suspected animal, procedures of wider use but time-consuming and often 



