497 
animal inoculation, biological test, serum agglutination reaction, 
and the tuberculin test are made use of in arriving at a definite opin- 
ion 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 
their impracticability, while the tuberculin test is most satisfactory 
and is the best diagnostic agent known for the disease. 
Tuberculin was invented by Koch in 1890, and was first used 
experimentally in treating tuberculosis in man. In these cases it 
was observed that its injection was followed by a rise of temperature, 
which led veterinarians to apply tuberculin to suspected animals to 
see if a similar reaction resulted. Numerous experiments showed 
this to be the case, and since 1891 the use of tuberculin as a diag- 
nostic agent for tuberculosis of cattle has been almost universally 
adopted in all parts of the civilized world. No one thinks of accept- 
ing tuberculin as an absolutely infallible agent, but it is immeasura- 
bly more dependable than any other method that has ever been used. 
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 
substance is injected under the skin of an animal it is absolutely una- 
ble 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 tem- 
perature will follow the use of tuberculin. In practice the tuberculin 
test is applied by first taking a sufficient number of temperatures at 
intervals of two hours to ascertain the normal variation of tempera- 
ture of the animal to be tested. The tuberculin is then injected 
hypodermically between 8 and 10 p.m. on the day of t aking the prelim- 
inary temperatures. On the following day the “ after’ 7 temperatures 
are recorded every two hours, beginning at 6 a. m. and continuing 
until twenty hours following the injection. As a result of this method 
an accurate diagnosis may be established in over 97 per cent of the 
cases tested. The relatively few failures in diagnoses are included 
among two classes of cattle. The first class contains those that are 
tuberculous, but which do not react either because of the slight effect 
of an ordinary-sized dose of tuberculin on an advanced case of the 
disease with so much natural tuberculin already in the system, or on 
account of a recent previous test with tuberculin which produces a tol- 
erance to this material lasting for about six weeks. . The-second class 
includes those that are not tuberculous, but which show an elevation 
of temperature as a result of (a) advanced pregnancy , (b) the excite- 
ment of oestrum, (c) concurrent diseases as inflammation of the lungs, 
intestines, uterus, udder, or other parts, abortion, retention of after- 
24907— Bull. 41— OS 32 
