666 ACTIVE IMMUNIZATION 



in each cubic centimeter 2 milligrams of solids, representing 10 milli- 

 grams of dried tubercle bacilli. 



3. Bacillen Emulsion (B. E.). This was a still later form of tuber- 

 culin made by Koch, 1 and, as its name indicates, it is an emulsion of 

 tubercle bacilli. The culture is grown as for O. T.; the bacilli are 

 filtered off, ground, but not washed, and one part of the pulverized 

 material emulsified in 100 parts of distilled water; an equal part of 

 glycerin is then added, making a 50 per cent, glycerin emulsion, each 

 cubic centimeter of which contains the immunizing substances of 5 mg. 

 of dried tubercle bacilli. Since B. E. was not washed, it was assumed 

 that it would retain all extractives and the entire contents of the bodies 

 of the tubercle bacillus. 



While Koch was preparing these various tuberculins others were 

 being made, one of which, prepared by Denys, is used extensively at 

 present in the treatment of tuberculosis. 



4. Bouillon Filtrate (B. F.). This is practically Koch's old tuber- 

 culin unheated. It is prepared in the same manner as O. T., except 

 that the bacillus-free filtrate a clear fluid said to contain only the 

 soluble secretions of the bacilli, plus the metabolized culture-medium 

 is not heated or concentrated and is ready for use without any further 

 modification. 



5. Beraneck's Tuberculin. This is a preparation for which its 

 inventor claims only minimal toxicity and a high content of specific 

 substances. It is prepared by cultivating the bacilli on a non-peptonized 

 5 per cent, glycerin bouillon medium, which is not neutralized. The 

 filtrate from this culture is known as T. B., or toxin bouillon. The 

 residue is shaken for a long time at from 60 to 70 C. with 1 per cent, 

 orthophosphoric acid. Equal volumes of the unheated toxin bouillon 

 and of the acid extract of the bacillary bodies are combined to form the 

 whole tuberculin. 



6. Von Ruck's Watery Extract. 2 This tuberculin has been widely 

 used in the United States. It is prepared as follows: Concentrate a 

 culture in vacuo at 55 C. to one-tenth volume (this requires about one 

 month). Filter through paper and then through porcelain. Pre- 

 cipitate with an acid solution of sodic bismuth iodid. Filter and neu- 

 tralize the acid solution. Filter again. Precipitate with absolute 

 alcohol to make 90 per cent, alcohol arid filter. Wash the precipi- 

 tate with absolute alcohol. Dry the precipitate and make a 1 per 



1 Deutsch. med. Wochenschr., 1901, xxvii, 839. 



2 Zeitschr. f. Tuberk., 1907, xi, 493. 



