356 INFECTION AND RESISTANCE 



to one-tenth the original volume. This 60 per cent, glycerin" extract 

 of the tubercle bacilli is then filtered clear and constitutes the tuber- 

 culin. 



The old tuberculin is a preparation which is extensively used 

 in the subcutaneous and intracutaneous tests upon human beings and 

 cattle, and forms the basis of the various preparations by von Pir- 

 quet, Moro, and others in the cutaneous tuberculin reactions. In 

 his earliest work von Pirquet used a 25 per cent, solution of the old 

 tuberculin. At present an undiluted old tuberculin is used for these 

 purposes. 



The old tuberculin also is the material from which the prepara- 

 tion for the ophthalmotuberculin test is made. For this purpose 

 Calmette advises precipitating old tuberculin with double the volume 

 of 95 per cent, alcohol, allowing the precipitate to settle and repeat- 

 edly washing the sediment with 70 per cent, alcohol. The powder 

 which results is thoroughly dried, pulverized, and made up for use 

 in 0.5 per cent, solutions. Bandelier and Roepke recommend the 

 use of the diluted old tuberculin directly for these tests, employing 

 a 1 per cent, solution. 



TUBERCULIN (T R AND T O) 



The description of the preparation of these tuberculins we take 

 from Ruppell in the Lancet, March 28, 1908. Virulent cultures of 

 tubercle bacilli are dried in the vacuum and are then thoroughly 

 pulverized by specially constructed machinery, and the grinding is 

 continued until no intact bacilli are found in the preparation. One 

 gram dry weight is then shaken up in 100 c. c. of sterile distilled 

 water. The mixture is then centrifugalized at high speed the 

 supernatant fluid is T O (tuberkulin oberschicht). This contains 

 the water-soluble substances of the bacillus and gives no precipitate 

 with glycerin. The residue T R (tuberkulin ruckstand) is again 

 dried and ground up, shaken up in water, and centrifugalized. This 

 is repeated 3 or 4 times, the total volume of water used for all the 

 repetitions not exceeding 100 c. c. At the end of several repetitions 

 all the T R goes into emulsion, and the various supernatant fluids 

 obtained during these repeated grindings and shaking are mixed 

 together and constitute the final T R preparation. This preparation,* 

 according to Koch, contains important antigenic substances, it gives 

 a precipitate with glycerin, and it is standardized by the determina- 

 tion of the solid substances contained in a cubic centimeter. This, 

 for a standard preparation, should be 0.002 gram to a cubic centi- 

 meter. 



