56 CITY MILK SUPPLY 



from eating cattle droppings for the grain they contain, or from being fed 

 on skim-milk from tuberculous cows. They may also become infected 

 with tuberculosis germs of the avian type from the droppings of fowls. 

 In the latter case the disease is usually of a local character while the 

 bovine bacilli give rise to a generalized infection. Wherever slaughter 

 houses keep record of the points from which the animals come and as to 

 whether they are tuberculous or not, there is afforded evidence that may 

 be utilized in tracing up diseased herds and in mapping regions that are so 

 generally infected that the animals coming therefrom may be expected to 

 be tuberculous. In this connection it should be said that range animals 

 are commonly pretty free from the disease, but of late years a tendency 

 for it to increase in this sort of stock has been noted. Thus reports of 

 meat inspectors in San Francisco and Los Angeles indicate that the pro- 

 portion of cattle from certain ranges which are affected with tuberculo- 

 sis has increased from 1 to 5 per cent, in the last five years. 



Viability of B. Tuberculosis in Butter and Ice Cream. Dairy products 

 are to some extent infected with the germs of bovine tuberculosis. Cream, 

 whether raised by gravity or separated, carries bacteria with it so that it 

 is natural for both butter and ice cream made from the milk of tubercular 

 cows to contain tubercle bacilli since neither the salting of the butter 

 nor the freezing destroy the microbes. 



Briscoe and MacNeal have compiled a list of 39 investigations of the 

 butter of 24 European and one American city; out of 1,233 samples 163 

 or 13.2 per cent, were infected with the germs of tuberculosis. They found 

 that two out of six samples of butter from Urbana, 111., examined, carried 

 the bacilli. By experiment they found that tuberculosis germs sur- 

 vive in a virile condition for a much longer period than the butter is usu- 

 ally held in cold storage. This is in line with Mohler's statement that 

 tubercle bacilli retain their virulence in butter made in the usual way 

 and stored under ordinary market conditions until time of sale. It should 

 be mentioned that butter made from carefully pasteurized cream does not 

 carry tuberculosis germs. 



Viability of B. Tuberculosis in Oleomargarine. In the usual way of 

 making oleomargarine in the United States the fat used is comminuted at 

 not over 122F. for 1% hr. Then sour milk is added and the whole mass 

 thoroughly mixed ; dairy butter is next added and a certain proportion of 

 vegetable oils. Next, enough more oils are added to lower the tempera- 

 ture to that of dairy butter. Therefore, opportunity is afforded the prod- 

 uct to be infected in three ways, viz. : (1) by the fat from the cattle, for 

 tubercle bacilli will withstand a temperature of 122F. for some hours; 

 (2) from the butter and sour milk that is added; and (3) in the process of 

 manufacture it may be contaminated by tuberculosis germs of human 

 origin. Briscoe and MacNeal enumerate seven investigations of oleomar- 



