TUBERCULOSIS. 419 



of these bacilli, but no living bacilli; 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 tem- 

 perature will follow the use of tuberculin by the subcutaneous 

 method. This substance, discovered by Koch, has the effect, when 

 injected into the tissues of a tuberculous animal, of causing a decided 

 rise of temperature or other manifestations while it has no such 

 effect upon animals free from the disease. The value of tuberculin 

 for this purpose was tested during the years 1890 and 1891 by Gutt- 

 man, Roeckl and Schiitz, Bang and Salomonsen, Lydtin, Johne and 

 Siedamgrotzky, Nocard, and many others. It was at once recognized 

 as a most remarkable and accurate method of detecting tuberculosis 

 even in the early stages and when the disease had yet made but little 

 progress. It is now quite generally employed. 



The tuberculin test came into existence through the most careful 

 and thorough scientific experimentation. 



As a result of its use an accurate diagnosis may be established in 

 more than 90 per cent of the cases tested. The relatively few fail- 

 ures 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 tolerance to this material, last- 

 ing for about six weeks. The second class includes those that are 

 not tuberculous, but which show indications of a reaction as a result 

 of (a) advanced pregnancy, (h) the excitement of oestrum, (c) con- 

 current diseases, as inflammation of the lungs, intestines, uterus, 

 udder, or other parts, abortion, retention of afterbirth, indigestion, 

 etc., (d) inclosure in a hot, stuffy stable, especially in summer, or 

 exposure to cold drafts or rains, (e) any change in the method of 

 feeding, watering, or stabling of the animal during the test. Not- 

 withstanding all these possibilities of error, the results of thousands 

 of tests show that in less than 3 per cent of the cases tested do these 

 failures actually occur. In the first class the chances of error are 

 decidedly reduced by the skilled veterinarian by making careful 

 physical examination and diagnosing clinically these advanced cases, 

 and by the injection of double or triple doses into all recently tested 

 cattle, with the taking of the after-temperature, beginning two hours 

 following the injection and continuing hourly for 20 hours. 



It is therefore apparent that tuberculin should be applied only 

 by or under the direction of a competent veterinarian, capable not 



