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cipitins for the specific hemoglobin only, and not agglutinins, opsonins, or lysins for 

 the red blood cells. Hektoen and Schulhof did not think that the antigen in ques- 

 tion was hematin, but considered it possible that it was adsorbed by the hemoglobin 

 molecule, or that it was a part of it which was split off by the acetic acid used in 

 separating the hematin and globin, Bennett and Schmidt and Hektoen and Schulhof 

 have reminded us that the red blood cells probably contain many antigens. Besides 

 those demonstrated by them in extracts of washed laked cells, there are probably 

 others in the stroma which are yet unaccounted for. 



Other complex materials commonly used as antigens have similarly received 

 analytical study. As early as igoi several workers separated casein from milk and 

 established its antigenic individuality by means of precipitin reactions. In 1918 

 Osborne and Wakeman^ isolated four chemically different proteins from milk, and 

 Wells and Osborne- showed them to be immunologically distinct by means of the 

 anaphylaxis reaction. 



Wells^ separated four proteins from egg white: albumin, globulin, ovomucoid, 

 and a substance common to both albumin and globulin; and also a protein from the 

 egg yolk: ovo-vitellin. By producing anaphylaxis in guinea pigs he showed all of 

 these to be good antigens, and quite distinct from one another except for the sub- 

 stance common to both albumin and globulin. 



In a series of papers on the biological reactions of vegetable proteins Wells and 

 Osborne,'' working with many kinds of seeds, have shown that there may be, in the 

 same seed, a number of proteins which are chemically and immunologically inde- 

 pendent. The same seed may contain several globulins besides albumin and the very 

 soluble non-coagulable proteins which have been termed "plant proteoses." All of 

 these are antigenic. Very few ordinary antigens have been overlooked in these 

 analytical studies. Even from horse dandruff two proteins have been isolated. ^ 



Most attempts to isolate toxins have not been especially successful, and there 

 is no general agreement upon their chemical structure. Most of the preparations 

 give the color reactions for proteins, but there seems to be no relation between the 

 intensity of these reactions and the activity of the toxin. Some have not given 

 the usual protein reactions, but this may possibly mean that the toxin is powerful 

 enough to show activity in quantities too small to be detected by the color tests used. 



Perhaps the most complex of the antigens in common use are bacteria, since uni- 

 cellular micro-organisms must necessarily contain everything needful for life, growth, 

 and reproduction. Recent investigations have kindled interest in finding out what 

 constitutes the antigenic part of bacterial cells. The micro-organism that has re- 

 ceived the most intensive study has been the tubercle bacillus. Its analysis has been 

 approached from various angles, and several fractions for which antigenic activity 

 has been claimed have been derived. 



' Osborne, T. B., and Wakeman, A. J.: J . Biol. Clieiu., 33, 7 and 243. 1918. 



^ Wells, H. G., and Osborne, T. B.: /. Infect. Dis., 29, 200. 1921. 



J Wells, H. G. : ibid., 9, 147. 1919. 



^ Wells, H. G., and Osborne, T. B.: ibid., 8, 66. 1911; 12, 341. 1913; 17, 259. 1915; 19, 183. 1916. 



s Longcope, W. T., O'Brien, D. P., and Perlzweig, W. A.: J. Immunol., 11, 253. 1926. 



