THE PROTECTION OF THE HERD 293 
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 must 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 detect 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 cer- 
tain 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 tuberculzn. In- 
asmuch as it does not contain any living bacilli, it cannot possibly 
cause the disease, and its use among animals cannot incite tuber- 
culosis, as has sometimes ignorantly been claimed. 
Although containing no bacilli, tuberculin does contain the 
toxins which the bacilli produce, and these toxins, if inoculated 
into an animal in sufficient quantity, would poison it. When 
injected in small quantity, the material has no effect upon the 
healthy individual; but if the individual is already affected with 
the disease, this inoculation produces a marked rise in temperature, 
which soon disappears. 
The fact that the injection is followed by a rise in temperature 
makes it possible for this material to be used among cattle in detect- 
ing tuberculosis. Healthy animals fail to respond to this inocula- 
