27 



BULLETIN OF 

 MASSACHUSETTS BOARD OF AGRICULTURE. 



VETEBINABY. 



Tuberculin. — What it is ; How it is used ; What it does. 



What it is. 



Tuberculin is the sterilized and filtered glycerine extract of the 

 bacillus tuberculosis It contains an active principle, chemically 

 complex in its composition, which is produced by the functional 

 activity of the germ. 



The first step in its preparation is the cultivation in the labora- 

 tory upon suitable nutrient material of large numbers of the germs. 

 These by their growth produce the active principle. The culture 

 is then treated with glycerine, filtered through porcelain to remove 

 the living germs, after which it is sterilized by being subjected to 

 the action of a high temperature. To make it more concentrated, 

 a part of the fluid is evaporated at a low temperature, and carbolic 

 acid added as a preservative. 



By the process of filtration and sterilization all germs in the 

 culture are either removed or destroyed, while the product of their 

 growth remains active in the tuberculin. 



As the active principle is not living matter, and can in no way 

 produce such, the injection of tuberculin into the system of a 

 healthy animal cannot by any possible means give rise to the dis- 

 ease tuberculosis. 



How it is used. 



To be accurate, the temperature of the animal to be tested 

 should be taken several times, at intervals of two or three hours, 

 during the- day, by inserting into the rectum an ordinary fever 

 thermometer. The last reading should be taken late in the after- 

 noon or during early evening. The several readings are for the 

 purpose of finding the normal temperature previous to the employ- 

 ment of the tuberculin. Ordinarily, with animals under normal 

 conditions, it is hardly necessary to take more than two or three 

 readings, the last of which should be made just before the tuber- 

 culin is used. A careful record of all temperatures should be 

 kept, and should any be found higher than normal, the testing 



