WHAT IS TUBERCULIN? 193 



animals can be detected by a physical examination. In many 

 cases only a few symptoms can be determined, and these are not 

 characteristic, as they may also occur in other diseases. The 

 tuberculin test is very accurate and when skillfully employed 

 detects the diseased animals practically without fail. 

 .( What Is Tuberculin? — Tuberculin is a fluid containing the 

 products (toxins) of the tubercle germ without the germs them- 

 selves, therefore when tuberculin is injected into healthy cattle, 

 it cannot cause tuberculosis. Tuberculin injected into tuber- 

 culous animals causes a marked temperature disturbance. The 

 tuberculin test may be applied by three different methods: (1) 

 The subcutaneous or temperature test; (2) the ophthalmic test, 

 and (3) the intradermal test. 



The subcutaneous test is the oldest method and the one most 

 commonly used, although the ophthalmic and the intradermal 

 tests are thought to be just as accurate. 



Tuberculin, when injected into diseased cattle, causes them 

 to become feverish within eight to sixteen hours after the tuber- 

 culin is administered. The fever lasts a short time and then 

 subsides. This temporary fever is called " the reaction," and 

 the animals so affected are called " reactors." 



In the subcutaneous test, the tuberculin is injected under 

 the skin, preferably in the region of the neck. Two or three 

 temperatures are taken, two or three hours apart, before the 

 tuberculin is injected in order to ascertain the animal's normal 

 temperature. Eight or nine hours following the administration 

 of the tuberculin, the temperatures are again taken every two 

 hours until six temperatures have been recorded. The animals 

 which are found to be feverish are regarded as being tuberculous. 



The ophthalmic test consists in inserting a drop of tuberculin 

 into the eye of the suspected animal. If the animal is healthy, 

 no change takes place, but if affected with tuberculosis, the eye 

 becomes reddened and waters profusely. 



The intradermal test consists in injecting a very small 



amount of tuberculin into (not under) the thin folds of the skin 



at the base of the tail. A reaction consists of the appearance of 



a swelling about the size of a walnut at the site of injection, 



13 



