CHEMICAL CONSTITUENTS 241 



its physical characters and the dependence of its heat stability on 

 the hydrogen ion concentration of the substrate, the authors sug- 

 gested that this antigen might be closely related to the antineuritic 

 water-soluble B vitamin. 



In another communication (1925), Perlzweig and Keefer 1080 re- 

 ported a method for purifying the antigen but gave no details of 

 its immunological properties. From massive cultures in Huntoon's 

 medium, after heat-killing and filtration, the antigenic substance 

 was separated from non-antigenic material by ultrafiltration 

 through collodion. Further purification was effected by precipita- 

 tion at the isoelectric point (pH 4.1) with 0.1N acetic acid- 

 sodium acetate buffer mixture. The precipitate was dissolved in 

 water with the addition of a small amount of 0.1N sodium hy- 

 droxide. The preparation contained 20 milligrams of nitrogen per 

 100 cubic centimeters (based on the volume of the original solu- 

 tion), which might indicate that it was made up, in part at least, 

 of the nitrogen-containing specific carbohydrate of Type I Pneu- 

 mococcus, the organism used as source material. Since Perlzweig 

 and Keefer gave no other details, it is impossible to judge the pu- 

 rity of their antigen, but Perlzweig and Steffen, 1081 in a 1923 re- 

 port, considered that it existed in a loose chemical or physical un- 

 ion with protein. It is to be presumed, therefore, that the authors 

 had not isolated the polysaccharide in pure form, but rather the 

 carbohydrate-protein compound from which some of the protein 

 had been removed. 



At about the same time, Zinsser and Parker, 1583 continuing the 

 study made by Zinsser 1575 on tuberculin, described an antigen ob- 

 tained from Pneumococcus and other bacteria which was analo- 

 gous to, if not identical with, the substance isolated by Dochez 

 and Avery. 321 These "residues" or "residue antigens" were pre- 

 pared in the following manner: Pneumococci were grown on agar, 

 removed from the medium and dried, then shaken with salt solution 

 at a pH of 9.0 to 9.4, and immediately used or neutralized and 

 stored. The extracts were centrifuged, passed through a Berkefeld 



