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THE ORIGIN OF THE TUBERCULIN TEST. 
Tuberculin was invented by Koch in 1890, and was first used ex- 
perimentally 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 diagnostic 
agent for tuberculosis of cattle has been almost universally adopted 
in all parts of the civilized world. Xo one thinks of accepting tuber- 
culin as an absolutely infallible agent, but it is immeasurably more 
dependable than any other method that has ever been used. 
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 
substance 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 tem- 
perature 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 
ascertain 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 the “ after ” temperatures are recorded every two hours, begin- 
ning at 6 a. m. and continuing until twenty hours following the 
injection. 
THE RELIABILITY OF THE TUBERCULIN TEST. 
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 diagnosis 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 previous test with tuberculin 
which produces a tolerance to this material lasting for about six 
a The ophthalmo-tuberculin test and the cuti-tubercnlin test, as their names 
imply, consist in the application of the tuberculin to the eye and to the scarified 
skin of the animal to be tested. These methods will not be discussed at present, 
as they are still in the experimental stage. 
