NATURE OF ANTIBODIES 195 



terial antibodies. Heidelberger and Avery found that such sub- 

 stances in pneumococci are polysaccharides. It is now known that 

 high molecular carbohydrates are important as determinants of 

 specificity of many bacterial agglutinin and precipitin reactions 

 (Landsteiner, 1936, p. 44) and Schiff and Adelsberger* seem to 

 have shown that human red cell haptens are either complex poly- 

 saccharides or lipoid-carbohydrate combinations. Landsteiner and 

 his associates have shown that a wide variety of substances may 

 function as haptens (see Chapters XVII and XVIII). 



In a later chapter attention is caUed to the conception of 

 Ehrlich supported by experimental proof of WeUs and Osborne that 

 antigenic specificity depends upon the chemical constitution of 

 the antigen. Landsteiner (1936, p. 73-74) calls attention to the 

 possibility of a single antigen having several reacting groups 

 and that, therefore, a number of antibodies may be formed for one 

 antigen. He and van der Scheer (1938) have also shown that 

 separate antibodies may be formed for portions of an antigenic 

 molecule. It is apparently established that cells contain many 

 antigenic factors, and it is thought that the cell antigens present 

 a mosaic structure. It is apparent that the surface antigenic 

 factors will play a more important role in serological reactions 

 than antigenic factors buried beneath the surface. Their poten- 

 tialities may be masked. For a more extensive discussion of the 

 complex nature of antibodies the student is referred to a paper by 

 Marrack and Carpenter (1938). 



Nature and Origin of Antibodies.— The immunologists have 

 found that the antibodies are precipitated with the euglobulin or 

 pseudoglobulin fractions of serum. According to Landsteiner 

 (1936, p. 94) it is not yet decided whether antibodies are proteins 

 or substances intimately bound to tlie proteins. There is strong 

 evidence indicating that they are protein in nature and therefore 

 are frequently called antihody-glohulins or immune-glohtdins. They 

 unite readily with their antigen at 0° C, are not dialyzable, and 

 resist drying for long periods of time. 



Fahey and Green (1938) obtained from normal horse serum 

 three water-insoluble proteins (euglobulins) by isoelectric precipi- 

 tation in a very low salt concentration. They named these Pj, Pn, 

 and Pi 1 1 fractions. In a second communication Green, McKhann, 

 Kapnick and Fahey applied the same methods to a study of frac- 



•See discussion by Landsteiner (supplementary references). 



