TUBERCULINS 



371 



both in size and number, the broth remaining perfectly 

 bright and clear. Sometimes a dry crinkled film forms 

 on the surface of the broth, and may spread all over it, 

 and tends to creep up the sides of the vessel. The virulent 

 organism from the primary cultivations is difficult to 

 grow on anything but glycerinated 

 potato, egg medium, serum, or brain 

 agar. 



TUBERCULINS. Extracts of, and sus- 

 pensions of, triturated tubercle bacilli, 

 human or bovine, known as " tuber- 

 culins," are employed in treatment 

 and for the diagnosis of tuberculosis. 

 Tuberculin is frequently designated by 

 a capital T, and that prepared from a 

 bovine strain has a capital P prefixed 

 (P = = perlsucht). Thus PTR means 

 new tuberculin prepared from a bovine 

 strain. 



Old tuberculin (Syn. TO or TA = tuber- 

 culin original alt). This is prepared 

 by growing the tubercle bacillus in 

 glycerin veal broth in a shallow layer JT JG 40. _ Tubercle 

 in flat flasks (Fig. 41), so that there is bacillus. Glycerin- 

 a free supply of oxygen. After some a s ar culfcure three 



T . , . . , months old. 



weeks an abundant growth with copious 

 film formation develops ; the latter is essential, and occurs 

 only if some of the growth floats on the surface, but it 

 does not appear to matter whether the bacilli be virulent 

 or non- virulent, or whether they be of human or of 

 mammalian origin. The cultures, bacilli included, are 

 heated at 115 C. in the autoclave for half an hour, then 

 concentrated over a water-bath to about one-tenth of 

 their volume, and finally are filtered through porous 

 porcelain ; the resulting fluid is syrupy, owing to the 



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