270 AGRICULTURAL BACTERIOLOGY 



plants has increased in a most remarkable manner, due to 

 the development of methods of transportation. From north- 

 western Europe the improved breeds of cattle, sheep, 

 horses, and hogs have been shipped to all parts of the 

 world, and with- them have been carried the diseases with 

 which they were affected. Many countries into which such 

 diseases were thus introduced had been previously free 

 from them, and -could have been kept so if there had been 

 sufficient knowledge concerning the nature of these com- 

 municable diseases, their detection and mode of dissemina- 

 tion. This knowledge, in many instances, was acquired 

 only after the harm had been done. The United States is 

 still free from some of the communicable diseases that are 

 a cause of great loss to the farmers of Europe, and it be- 

 hooves us to use all possible precautions to prevent their 

 introduction into this country. 



The islands of Jersey and Guernsey are the only impor- 

 tant breeding centers that are free from tuberculosis, and 

 this condition has resulted from a rigidly enforced rule that 

 no live cattle should be imported on to these islands. The 

 percentage of animals affected with the disease ranges from 

 over 50 in some of the German states, as Safxony, to less 

 than 5 in our Western and Southern States. The disease 

 is not widespread in those sections in which cattle-raising 

 is not important and into which the improved breeds have 

 not been introduced in considerable numbers. In England 

 it is asserted that less than 5 per cent, of the milking herds 

 of Shorthorn, Ayrshire, and Jersey cattle are free from 

 tuberculosis, while in Wisconsin, one of the most impor- 

 tant dairy States in this country, not over one third of the 

 herds contain any tubercular animals. In the Eastern 

 States, in which dairying has been longer established, the 

 percentage of affected herds is higher. 



The rapid spread of the disease within recent years is 



