DAIRY ME:ETING. 85 



Xow this tuberculin, prepared in this way, was discovered to 

 have the ability to help us detect tuberculosis, and in this way : 

 A little of it, injected underneath the skin of an animal that is 

 diseased causes, in the course of some hours, a rise of tempera- 

 ture in the animal. That rise is gradual. It remains at a 

 maximum for a time and gradually declines. After the animal 

 is inoculated the rise of temperature and decline follow in the 

 course of 24 or 28 hours. The temperature has then returned 

 to the normal. That is what we call a reaction. If the animal 

 is sound the dose has no apparent effect. In this wav we diag- 

 nose the presence of tuberculosis. This test is so simple and so 

 €xact and so reliable that it has come to be the one test for 

 tuberculosis. We may make mistakes in diagnosing tuberculosis 

 by physical signs. We may find a lump in the udder that we 

 think is a tubercle, and it may not be a tubercle at all. Enlarged 

 glands may not be the result of tuberculosis. Cattle sometimes 

 are in a very unthrifty condition, and the cause is not tubercu- 

 losis at all. An expert can discover a good many cases by physi- 

 •cal examination, but even an expert makes mistakes ; and the 

 great majority of cases he cannot detect at all, no matter how 

 expert he is. Tuberculin is so exact in its ability to diagnose 

 that the early developing cases are discovered with quite as great 

 certainty as the later ones. And while it is not infallible, and 

 certainly not infallible when it is applied by fallible human 

 Tjeings, it is certainly by long odds the most effective way we 

 have. It has come to be regarded so in such an emphatic degree 

 that there is no state in the Union but that is using it. The 

 United States Government does not allow any cattle for breed- 

 ing or milk producing purposes to come into the country with- 

 out this test, and most of the states are as rigid in regard to 

 cattle crossing the State line. Our most progressive breeders 

 the world over are testing their animals in order to keep a knowl- 

 edge of their condition. 



MANNER IN WHICH THE DISEASE IS CONVEYED. 



How does tuberculosis spread from one animal to another? 

 How does the diseased animal convey the disease to well animals? 

 We have noticed that the germs must find their way into the well 

 •animals bv certain channels. How do thev find their wav out 



