TUBERCULIN TEST 215 



the lesions or to enable one to find the bacteria micro- 

 scopically. 



§ 155. Tuberculin test. The tuberculin test is the 

 best, and in a large majority of tuberculous cases among 

 animals and in man, the only means of positively detecting 

 the disease in the living individual. 



Tuberculin. Tuberculin is the concentrated liquid, us- 

 ually glycerinated bouillon, on which tubercle bacteria have 

 grown until the products resulting from their multiplication 

 have become imparted to the medium in sufficient quantity to 

 inhibit their further development. It is not definitely deter- 

 mined just what these products are or just how they are 

 elaborated. Briefly stated, the preparation of tuberculin con- 

 sists in the following procedure: 



1. The preparation of the culture medium (glycerinated 

 bouillon), distributing it in suitable flasks and inoculating it 

 with the growth from a pure culture of tubercle bacteria. 



2. The flasks are placed in an incubator at a temperature 

 of about 37" C. where they remain until the growth ceases. 

 The length of time necessary to accomplish this depends upon 

 the age and condition of the culture from which the inocula- 

 tions were made. From four to ten weeks are usually re- 

 quired. 



3. After the maximum growth is attained, the cultures 

 are sterilized by heat, either by boiling in a closed water bath 

 or heating to a higher temperature in an autoclav. 



4. After sterilization, the cultures are filtered to remove 

 all of the dead bacteria, and then the filtrate is evaporated 

 over a water bath to the desired degree. 



5. The concentrated liquid is passed through a Pasteur 

 or Berkefeld filter, standardized, bottled and labeled for dis- 

 tribution. It should be perfectly clear although its color may 

 vary. If it is cloudy it should be rejected. 



It will be seen from the method of preparation that tuber- 

 culin cannot possibly contain living tubercle bacteria. It is 



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