70 INFECTION AND RESISTANCE 



paring bacterial extracts for purposes of immunization and antigen 

 production in general as follows: 



A. Extraction of Bacteria by Permitting Them to Remain for 

 Prolonged Periods in Fluid Media 



The bacteria may be grown upon slightly alkaline bouillon and 

 kept at incubator temperature for one to two months. They are 

 then filtered through Berkefeldt or other suitable filters. This is the 

 common method of producing antigen for precipitin reactions, in fact 

 the method employed by Kraus in the discovery of the bacterial pre- 

 cipitins. It is by no means certain whether the antigens prepared in 

 this way represent simple extractions or autolytic products of the 

 bacteria; probably both processes take place. The antigenic value 

 of the fluids obtained in this way is never very great. From such 

 filtrates Brieger and Mayer, Pick, and others have attempted to 

 obtain the antigen in a purified form by chemical precipitation. 

 Pick 33 precipitates the bouillon filtrate by saturation with ammonium 

 sulphate; the precipitate is redissolved in water and again precipi- 

 tated with ammonium sulphate and the resultant precipitate dried 

 on a filter. It is then dissolved in water and precipitated with 

 alcohol. The sticky substance which comes down represents the 

 antigen. 



Suitable extracts can occasionally be obtained also by emulsify- 

 ing agar cultures in physiological salt solution and allowing them 

 to stand for twenty-four hours or more at incubator temperature. 

 In our own experience we have found this method rather inefficient 

 for yielding strong extracts. More efficient extraction is usually ob- 

 tained when the bacteria are suspended in alkaline fluids such as 



N 

 sodium hydrate. Lustig and Galleotti digest the bacterial mass 



for 24 hours with 1 per cent. NaOH, then precipitate with am- 

 monium sulphate, dry in vacuo and pulverize. 34 



Recently, also, Uhlenhuth 35 has employed the proprietary prep- 

 aration "antiformin" 36 for the production of antigens. This 



33 Pick. "Hoffmeister's Beitrage, etc./' Vol. 1, 1902. For an extensive 

 discussion of the various methods employed for the production of bacterial 

 antigens by chemical methods see Pick in Kraus und Levaditi, etc., Vol. 1, and 

 the same author in Kolle u. Wassermann, etc., 2nd Ed., Vol. 1. 



34 See Pick. Loc. cit. 



35 Uhlenhuth. Centralbl. f. Bakt. } I, Ref. Vol. 42, Beilage, p. 62. 



36 "Antiformin" is a substance largely employed for the cleansing of pipes 

 and vats of organic matter because of its powerfully solvent action. Its 

 value in concentrating tubercle bacilli out of sputum and other mixtures 

 depends upon its power to dissolve the tissue elements and all bacteria except 

 those that are acid-fast. Rosenau ("Preventive Medicine and Hygiene," 



