168 APPLIED IMMUNOLOGY 



tuberculin tests, the luetin test and the diagnosis of 

 typhoid and gonorrhoea! infection. 



Tuberculins. — Tuberculin has been prepared in 

 many ways and, although each preparation may be 

 used diagnostically as well as therapeutically, it is true 

 that one furnishes better results for diagnostic pur- 

 poses, just as others are superior from the therapeutic 

 standpoint. The available products include Koch's 

 " old " and " new " tuberculins, Denys' " bouillon fil- 

 trate," Spengler's " perlsucht," Dixon's " bacillary 

 extract," and Russian " tuberculinum purum." 



Old Tuberculin (" O. T.").— The original tuber- 

 culin made and used by Koch has been styled " old " 

 in contradistinction to his later or " new " tuberculins. 

 It is prepared from the five or six weeks' pure culture 

 of B, tuberculosis on five per cent, glycerin bouillon. 

 The culture medium is then evaporated to one-tenth 

 of its volume and filtered through porcelain. The 

 filtrate containing all the soluble secretion products 

 of tubercle bacilli is then diluted with glycerin, form- 

 ing a twenty-five or fifty per cent, solution. The 

 glycerin acts simply as a preservative, not as a germi- 

 cide. Hence the stock solution may become con- 

 taminated if frequently opened, and it should be steril- 

 ized before making dilutions by heating on a water- 

 bath for one hour at 60° C. or by boiling in a test- 

 tube for ten minutes. It is customary when making 



