PRECIPITINS 99 



Precipitins. Shortly after the discovery of the agglutinating power 

 of certain antisera, Kraus ascertained that such sera, when brought 

 together with the clear filtrates of the corresponding bouillon cultures, 

 will cause the appearance of a turbidity which gradually settles 

 at the bottom of the tube as a precipitate (1897). Further studies 

 then showed that this peculiar behavior is owing to the presence of 

 definite antibodies in the sera of the injected animals, and that such 

 antibodies are formed whenever foreign albumins either of animal 

 or vegetable origin are introduced through parenteral channels. 

 From their precipitating properties these substances have been 

 termed precipitins, while the corresponding antigen is termed 

 precipitinogen. 



Like the bacteriolysins, the precipitins have been shown to be 

 specific in their action, within certain limitations at least, and the 

 reaction has accordingly been used for the purpose of identifying 

 the origin of various albumins. In the form of the biological blood 

 test the principle is now generally utilized for the purpose of deter- 

 mining the origin of blood stains, and upon the same basis it has 

 been possible to establish zoological relationship between different 

 animals (see Precipitin Test.) 



Of special interest is the fact that a number of investigators are 

 now inclined to regard the agglutinating properties of the various 

 antisera merely as one form of expression of the more general pre- 

 cipitating qualities of the same sera, so that according to this con- 

 ception the agglutinins as antibodies sui generis would have no 

 existence. It is supposed that agglutination among cells corresponds 

 exactly to agglutination among dissolved albuminous particles, which 

 latter process leads to what we are accustomed to speak of as pre- 

 cipitation. This view is supported especially by Kraus, v. Pirquet, 

 and Wassermann. These observers could show that bacterial filtrates 

 are capable of binding agglutinin, and that the filtrates in question 

 must hence have contained agglutinable substances. This is well 

 brought out if cultural filtrates are added to a corresponding agglu- 

 tinating serum in sufficiently large quantity. Under such conditions 

 the serum may lose its agglutinins entirely. If insufficient amounts 

 of filtrate are used, on the other hand, the agglutinating titer remains 

 unaltered, the difference in behavior being explained by the assump- 

 tion that much smaller quantities of precipitin are required to cause 

 agglutination than to bring about precipitation. 



