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. 
