TUBERCULIN. 579 



preparations having similar properties, the use of "TA, TR 



*\ . r , , , j * 3- 3 and "TO." 



which has been proposed for diagnostic and cura- 

 tive purposes and for convenience in carrying out 

 the agglutination reaction. One of these, "TA," 

 is an alkaline preparation which is made by ex- 

 tracting cultures with 1/10 normal sodium hy- 

 droxid solution. Its diagnostic value was equal 

 to or exceeded that of tuberculin because of 

 the longer duration of the reaction. However, in 

 view of the fact that it contained undissolved 

 cells, which caused the formation of abscesses at 

 the point of injection, its use was not encouraged. 

 For purposes of immunization Koch prepared a 

 fluid which contained all the bacterial constituents 

 and which at the same time is readily absorbed 

 without abscess formation. For its preparation 

 dried masses of the organism are ground up in an 

 agate mortar; after suspension in distilled water 

 and centrifugation, the emulsion consists of two 

 layers. The overlying opalescent whitish fluid was 

 designated as "TO" (Tub er culm-Ob er s) . After 

 removal of the fluid from the precipitate the lat- 

 ter was again dried and ground, suspended in 

 water and centrifugated as before, and the process 

 repeated until none of the sediment remained. The 

 different fractions of fluid, except the "TO," were 

 combined to constitute "TR" (Tuberculin-Rest), 

 which is really an emulsion of minute fragments 

 of cells. It is readily absorbed and does not cause 

 the formation of abscesses. This is commonly 

 called Koch's "new tuberculin." Still another 

 preparation which Koch later devised for active 

 immunization and for convenience in performing 

 the agglutination test consists of dried and ground 

 up bacilli which are suspended in equal parts of- 



