854 CYCLOPEDIA OF LIVE STOCK AND COMPLETE STOCK DOCTOR. 



passing tubercle bacilli through the feces or by an occasional cough, 

 and thus endanger all the healthy cattle in the herd. Consequently such 

 aids to diagnosis as animal inoculation, biological test, serum reaction, 

 and the tuberculin test are made use of in arriving at a definite opinion 

 relative to the presence or absence of this disease. The value of all but the 

 last of these is discounted by the technique required and by their im- 

 practicability, while the tuberculin test is most satisfactory and is the best 

 diagnostic agent known for the disease. 



II. The Origin of the Tuberculin Test. 



Tuberculin was invented by Koch in 1890, and was first used experi- 

 mentally in treating tuberculosis in man. In these cases it was observed 

 that its injection w^as followed by a rise of temperature, which led veter- 

 inarians to apply tuberculin to suspected animals to see if a similar 

 reaction resulted. I'iumcrous experiments showed this to be the case, 

 and since 1891 the use of tuberculin as a diagnostic ageni for tuberculosis 

 of cattle has been almost universally adopted in all parts of the civilized 

 world. No one thinks of accepting tuberculin as an absolutely infallible 

 agent, but it is immeasurably more dependable than any other method 

 that has ever been used. 



III. The Nature and Application of Tuberculin. 



Tuberculin is the sterilized and filtered glycerin extract of cultures of 

 tubercle bacilli. It contains the cooked products of the growth of these 

 bacilli, but not the bacilli themselves. Consequently, when this sub- 

 stance is injected under the skin of an animal it is absolutely unable to 

 produce the disease, cause abortion, or otherwise injure the animal. In 

 case the injected animal is normal there is no more effect upon the system 

 than would be expected from the injection of sterile water. However, 

 if the animal is tuberculous, a decided rise of temperature will follow 

 the use of tuberculin. 



In practice the tuberculin test is applied by first taking a sufficient 

 number of temperatures, usually three, at intervals of two hours to ascer- 

 tain the normal variation of temperature of the animal to be tested. The 

 dose of tuberculin (which should always be specified on the label) is 

 then injected hypodermically between 8 and 10 p. m. on the day of 

 taking the preliminary temperatures. On the following day "after" 

 temperatures are recorded every two hours, beginning at 6 a. m. and 

 continuing until twenty hours following the injection. 



IV. The Value and Reliability of the Tuberculin Test. 



As a result of this method an a<'curate diagnosis may be established 

 in over 97 per cent of the cases tested. The relatively few failures in 



