PRECIPIT1N8. 235 



Phytoprecipitins are produced by immuniza- 

 tion with albuminous substances of plant origin, 

 as ricin and albumin from grains, and their action itins ' 

 is specific for the homologous substance. 



Zooprecipitins are obtained by immunizing with 

 animal albumins. Through the work of Wasser- 

 mann and Uhlenhuth, of Nuttall, and others, it 

 has been demonstrated as a general law that im- 

 munization with an albumin from whatsoever 

 source gives rise to the formation of a precipitin 

 which manifests its action only against the par- 

 ticular albumin used for the immunization. Hence, 

 the albumin of a particular serum, in some un- 

 known respect, is different from that of all others ; 

 it is special to the species. 



Immunization with milk causes the formation 

 of a precipitin which throws down the casein of 

 the milk used for injection, but not that of milk 

 from another species. The milk of the goat may 

 be differentiated from that of the cow by the use 

 of the lactoserum. 



Likewise, after the injection of egg-white a 

 precipitin is formed which is specific for the type 

 injected. 



Three substances are open to study in the pre- 

 cipitation reaction. First, the fluid or substance and C prec?pi 

 which is used for immunization ; it bears the name tttte 

 of precipitogen, i. e., the precipitin-producing sub- 

 stance, Second, the specific constituent of the 

 precipitating serum, i. e., the precipitin. Third, 

 the precipitate, which is a consequence of the reac- 

 tion between precipitogen and precipitin. We are 

 able to recognize in this instance the actual end- 

 product of a reaction, a condition which is not so 

 easily realized in other "immunity reactions." Tt 



