2l6 TUBERCUI.OSIS 



heated on two occasions to a temperature and for a length of 

 time far in excess of that required to destroy them, besides be- 

 ing passed through a filter capable of removing all bacteria. 



The original tuberculin or lymph of Koch was concen- 

 trated to one-tenth of the volume of the saturated culture. 

 This gave a thick, syrupy liquid owing to the presence of the 

 glycerin. The diagnostic dose which came to be recom- 

 mended for cattle of medium weight was 0.25 c.c. On ac- 

 count of its consistency as well as the minuteness of the dose, 

 it was found to be practicable to dilute this quantity with 

 seven parts of a diluent. A weak solution of carbolic acid 

 was ordinarily used. The difficulties and the danger of con- 

 tamination involved in making the dilutions in the field led to 

 the method of diluting the tuberculin in the laboratory before 

 sending it out. This has been the practice of the Bureau of 

 Animal Industry for a number of years. Equally as good re- 

 sults are obtained by concentrating the saturated culture to 

 the point where 2 c. c. contains an equivalent of the 0.25 c. c. 

 of the highly concentrated lymph. This process avoids the 

 necessity of dilutions and, with the addition of a few drops of 

 carbolic acid, the weaker solution keeps perfectly. 



Tuberculin in the dose necessary to bring out its diag- 

 nostic effect is harmless for healthy animals. Thousands of 

 observations that have been reported assure us of this fact. 

 Tuberculin is in daily use in every state in the Union, in 

 Canada and in every country of Europe, yet so far as can be 

 learned not a single case of injury following its use has been 

 reported. In the tuberculous animal it produces a rise of tem- 

 perature which, within certain limits, follows a definite course 

 usually terminating in from 18 to 24 hours after the injection. 

 Occasionally the temperature remains above the normal for a 

 longer time. The temperature usually begins to rise in about 

 eight hours giving a steady but quite rapid elevation for from 

 I to 3 hours, a continuous high elevation for from 2 to 4 hours, 

 possibly longer, and a gradual decline. This is practically 

 constant, be the raise moderate or extreme. In addition to 

 the elevation in temperature there is sometimes a marked 



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