118 ILLINOIS STATE DAIRYMEN'S ASSOCIATION 



Methods of Diagnosis. 



Microscopic examinations of sputum, milk, and bowel 

 discharges of an animal are sometimes made to determine 

 the presence of tubercle bacilli and to diagnose tuberculosis, 

 but after many years of experience the tuberculin test is 

 now considered to be the most practicable and satisfactory 

 way of discovering the disease in the living animal. The 

 inoculation of guinea pigs with emulsions made from milk 

 or discharges from the living animals is sometimes resorted 

 to as a means of diagnosis, but that method of examination 

 is technical and requires special scientific training and 

 equipment. Besides, cases of tuberculosis may be over- 

 looked when laboratory methods are used, because tuber- 

 culous animals do not always discharge the tubercle bacilli. 



The Tuberculin Test. 



Testing animals with tuberculin is the process of intro- 

 ducing tuberculin into the animal and interpreting results 

 according to well-known standards. Tuberculin is a labor- 

 atory product prepared scientifically and, when of standard 

 potency and in the hands of skilful persons, it is a reliable 

 agent for detecting tuberculosis in animals. It contains no 

 living tubercle bacilli but is a product of the growth of 

 tubercle bacilli properly mixed with a substance on which 

 it has grown and properly diluted and preserved. No harm 

 can result to healthy animals from the proper application 

 of tuberculin even if doses many times greater than the reg- 

 ular ones are used. 



The use of tuberculin by untrained persons is to be dis- 

 couraged for the reason that in many cases its effect on tu- 

 becrulous animals is unobserved and not understood by 

 those unfamiliar with its action. Tuberculin, by its immu- 

 nizing property, can cause tuberculous animals to fail to 

 respond to its application at another time; therefore it may 

 be misused by unscrupulous persons. 



The Subcutaneous Test (Under the Skin). 



The subcutaneous test is made by injecting the proper 

 quantity of tuberculin underneath the skin into the subcu- 



