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. 



Ticbercidin. Tuberculin is the concentrated liquid, us- 

 ually crlvcerinated bouillon, on which tubercle bacteria have 

 grown^;ntil 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 iust 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 .7= C. where they remain until the growth ceases. 

 The lenc^ih of time necessary to accomplish this depends upon 

 the ac^e^nd condition of the culture from which the inocula- 

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



quired. 



. \fter the maximum growth is attained, the cultures 

 are sterihzed bv heat, either by boiling in a closed water bath 

 or heating to a higher temperature in an autoclav. 



, \fter sterilization, the cultures are filtered to remove 

 allot the dead bacteria, and then the filtrate is evaporated 

 over a water bath to the desired degree. 



, The concentrated liquid is passed through a Pasteur 

 orBerkefeld filter, standardized, bottled and labeled tor dis- 

 tribution. It should be perfectly clear although its color ma> 

 varv If it is cloudv it should be rejected. 



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

 culin cannot possibly contain living tubercle bacteria. It is 



