88 PRACTICAL DAIRY BACTERIOLOGY 



to the dairy industry. It is known to be present and increasing 

 in our dairy herds. 1 It is known that in the more thickly settled 

 parts of this country, as well as in Europe, the percentage of 

 the disease among cattle is quite large, although it is difficult 

 to give exact percentages. In Denmark and Germany 40 to 

 50 per cent, of the cattle are affected. In cold climates where 

 the cattle are kept housed much of the time it is more common 

 than in warm countries where they remain out of doors. In 

 America it does not yet appear to be as common as in Europe; 

 but still in the dairy districts of this country it is also very com- 

 mon* It is apt to run through a whole herd after it once gets 

 a foot-hold. Sometimes practically every animal in a herd will 

 have the disease, while in another herd none will be found. 

 With such wide differences averages mean little. The disease 

 is frequently introduced into a herd by the purchase of stock 

 that appears to be healthy but is really infected with the dis- 

 ease. Hence, highly bred stock is most likely to be found 

 infected. 



Statistics have also shown that the disease has been rapidly 

 increasing among cattle in the last 25 years. Such statistics, 

 it is true, are open to some criticism. 25 or even 15 years ago 

 the importance of tuberculosis in cattle was not recognized, 

 and the method of detecting the presence of the disease was 

 uncertain; careful records as to the percentage of tuberculosis 

 among cattle were then scanty and unreliable. It is only about 

 15 years ago that any very strenuous attempt was made to 

 determine the percentage of tuberculosis among cattle. As 

 years have passed the importance of the matter has drawn 

 more attention to it, and statistics have been collected with 

 more and more thoroughness and completeness. Such in- 



1 Salmon. 20th Ann. Rep. Bu. An. Ind., p. 89, 19Uj. 



Salmon. Bui. 53, Bu. An. Ind., 1904. 



Salmon. Bui. 38, Bu. An. Ind., 1906. 



Salmon. Bui. 33, Bu. An. Ind., 1901. 



