BOVINE TUBERCULOSIS I 69 



injurious to tliemselves and which in many cases check 

 their growth or otherwise affect them unfavorably. Tuber- 

 culin is such a product of the tubercle bacilli. It is made 

 in the laboratory by cultivating the bacilli in a suitable cul- 

 ture fluid, in which they, during their growth, produce this 

 new substance called tuberculin, which is dissolved in the cul- 

 ture fluid. The bacilli are then killed and filtered out of the 

 liquid, which, properly diluted, constitutes the tuberculin as 

 used for testing. If a small quantity of tuberculin is injected 

 under the skin of a healthy animal no appreciable change 

 takes place, but if the animal is at all afiected with tubercu- 

 losis there is, after a few hours, a rise of several degrees in the 

 animal's temperature ; this is called the reaction. If the rise 

 of temperature is two degrees or more it is looked upon as 

 evidence that the animal is tuberculous. 



The following is the usual method of procedure in testing 

 an animal : The normal temperature is taken in the rectum 

 with a specially constructed thermometer, once or twice before 

 injecting the tuberculin. About two cubic centimetres — 

 about a teaspoonful — is by means of a hypodermic syringe in- 

 jected beneath the skin in the region of the neck or shoulder. 

 It is desirable that ten or twelve hours should intervene between 

 the injection of the tuberculin and the subsequent taking of 

 the temperature ; so for convenience it is customary to make 

 the injections at night and to begin taking the temperatm^es the 

 next morninof. Thev are taken four or five times at intervals 

 of two hours. As indicated above, if the animal is tubercu- 

 lous we expect, sometime during the twenty-four hours 

 following the injection, a rise of temperature of two degrees or 

 more. 



Very extended use of tuberculin in this countrv as well as 

 abroad has demonstrated that it is a reliable and satisfactory 

 test for the presence of tuberculosis ; its percentage of failures 

 is small. It sometimes fails to produce the characteristic reac- 

 tion in very advanced cases — such cases as would be most 

 readily diagnosed without its use. On the other hand, it 

 detects cases not discoverable by any other means. Tiiere is 

 abundant testimony that its use is not in any way injurious to 

 a healthy animal. 



