THE PROTECTION OF THE HERD. 271 



cattle. Our agriculturists, by overfeeding with certain kinds of 

 food, and by special high breeding for the purpose of increasing the 

 yield of milk, are trying to turn an animal into a milking machine. 

 The highly bred animals are, of course, useful for the purpose for 

 which they are bred; but the agriculturist must remember that he 

 cannot turn his cow into a simple milking machine without suffering 

 some evil results from the change in her nature. In short, if the 

 cattle owner will learn that cattle are animals and not machines 

 and that they need something besides food and water to keep them 

 active, he will probably soon find the tendency to tuberculosis 

 becoming less. 



THE PROTECTION OF THE HERD. 



While the treatment of the cow as an animal and not a milking 

 machine must be the foundation of a healthy herd, the care of the 

 farmer most not stop there. The animals must be guarded against 

 infection and to this end much attention has been given in recent 

 years. 



The Tuberculin Test. Any method of protecting a herd against 

 tuberculosis must start with some method of detecting the disease 

 in animals. Certain forms of the disease, especially when in an 

 advanced stage, are easily discovered by clinical means, the 

 veterinarian being able to detect them by the examination of the 

 cattle. But there are other cases where no visible signs appear, 

 and these cannot be found by clinical means. The tuberculin 

 test has been devised to meet this difficulty and to dectect even the 

 mildest cases. Tuberculin was first prepared by Koch. It is 

 made by causing the tubercle bacilli to grow in a broth containing 

 glycerin. While growing in such a broth, the bacilli produce certain 

 toxic products which are soluble and which dissolve in the broth. 

 The material is then treated in such a way as to remove the bacilli, 

 and the clear, toxic-holding solution is tuberculin. Inasmuch 

 as it does not contain any living bacilli, it cannot possibly cause the 

 disease, and its use among animals cannot incite tuberculosis, as 

 has sometimes ignorantly been claimed. 



