PRECIPITOGEN. 239 



Precipitogen may be defined as any albuminous Nature of 

 substance immunization with which will cause the 

 formation of a specific precipitating serum. In 

 addition to those mentioned above, albuminous 

 urine, pleural exudates, ascitic fluid and that from 

 hydrocele are precipitogens. The same is true of 

 some albuminous fractions of serums, as globulin, 

 the precipitating serum for which may be called 

 antiglobulin. Kraus believes that the precipitogen 

 of bacterial filtrates is associated with albuminous 

 molecules. Jacoby obtained by tryptic digestion 

 of ricin, a precipitogen which gives no albumin 

 reaction. On the other hand, certain precipito- 

 gens are destroyed by pepsin and trypsin, a fact 

 which indicates their albuminous nature. 



Certain precipitogens are said to consist of a 

 thermolabile and a thermostabile portion, the dif- 

 ferentiation of which we need hardly consider. 



It is of no little interest that precipitogen, simi- 

 lar to precipitin, consists of two groups, through 

 one of which it unites with precipitin, whereas the 

 other has a coagulating function. Egg albumin, 

 for example, when heated to rather high tempera- 

 tures, loses its ability to participate in the pre- 

 cipitation reaction, although it retains its binding 

 power for precipitin. In view of the fact that the 

 two substances which enter into the reaction have 

 similar structures, it is difficult to say which as- 

 sumes the passive and which the active role. De- 

 generated precipitogen is also called precipitoid. 

 In order to distinguish the two precipitoids one 

 must speak of the precipitoid of precipitogen, and 

 the precipitoid of precipitin. The precipitoid of 

 precipitogen yields precipitin by immunization; 

 hence, it is all the more analogous to the toxoids. 



