CHAPTER LXI 

 PRECIPITINS AND THEIR APPLICATIONS 



H. M. POWELL 



Eli Lilly and Company, Indianapolis 



INTRODUCTORY 



Following closely upon the demonstration of antibody causing the specific clump- 

 ing or agglutination of cellular antigens came the description of antibodies causing 

 precipitation of unformed protein materials employed as clear solutions. Kraus' found 

 that cleared bacterial filtrates are antigenic, and that corresponding antibody can 

 readily be obtained from properly treated animals. When suitable mixtures are made 

 of precipitinogen and the artificially incited precipitin, precipitates result. The reac- 

 tion was found to be relatively specific, and various uses were suggested for the 

 precipitin reaction including species determination of micro-organisms, species sources 

 of proteins, serum diagnosis, etc. There was little hesitancy in assigning a new name, 

 the "precipitins," to the specific agents of such sera. Later work, however, has indi- 

 cated that the mere precipitation may be a secondary issue and the antibody in 

 question not a "precipitin" but a lytic antibody. 



Especially interesting were the observations that each antiserum reacted for the 

 most part only with the homologous antigen. The reaction, then, is in conformity with 

 other antigen-antibody reactions previously described in that specificity, perhaps one 

 of the most fundamental cornerstones of immunity, is a marked characteristic. 



It may be supposed that the reactions leading to the appearance of the visible 

 precipitate, the ring or the flakes, are closely similar to those initiating agglutination 

 of cellular antigens. A marked distinction is the degree of fineness of precipitinogen 

 as contrasted with the cellular antigens in agglutination reactions. Extensive lists of 

 substances encountered throughout the field of biology have the property of inciting 

 precipitin on injection into suitable animals. This is true also of the antigen con- 

 cerned in agglutination. 



PRECIPITINOGEN 



The antigenic nature of precipitinogen appears to be closely linked with its pro- 

 tein nature. The material may be desiccated and only extraction will release it, or it 

 may be very old. If it is intact protein it may still act as an antigen. Many at- 

 tempts toward more or less completely modifying precipitinogen, i.e., so it may no 

 longer give "protein reactions," have resulted in alteration of antigenic power or even 

 in its destruction altogether. Any procedure certainly destroying protein is also de- 

 structive of precipitinogen. In a great many experiments in this field it appears 

 doubtful whether non-protein material alone can act as precipitinogen. Ultimately it 

 would be difficult to eliminate in this connection combination between any non- 



• Kraus, R.: Wien. kiln. Wchnschr., lo, 736. 1897. 



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