68 IMMUNE SERA. 



as well as Stern, were able to show that the serum 

 of rabbits treated with guinea-pig serum is a 

 preeipitin also for the serum of monkeys. Prob- 

 ably this is because the sera of guinea-pigs and of 

 monkeys possess common receptors. For this rea- 

 son also the injection of a serum from one animal 

 into a closely related animal does not excite the 

 production of a preeipitin, e.g., the serum of chickens 

 injected into pigeons or that of rabbits into guinea- 

 pigs. We may assume that in these closely related 

 animals the serum of the one fails to find receptor 

 groups with which to combine; on the contrary, it 

 finds groups similar to its own, and these cannot 

 react on one another. In line with this is the work 

 of Uhlenhuth, who showed that the serum of ani- 

 mals treated with chicken egg albumin is a pre- 

 eipitin for egg albumin of other closely related 

 birds. 



Practical Application. These precipitins have very 

 recently found a practical application. Fish, Ehr- 

 lich, Morgenroth, the author, and Schiitze inves- 

 tigated the specific action of lactoserum. They 

 found that a serum derived by treating an animal 

 with cows' milk contained a preeipitin which reacted 

 only on the casein of cows' milk, but not on that of 

 human milk or goats' milk. The serum of an ani- 

 mal treated with human milk was specific for the 

 casein of human milk, etc. Ehrlich, Morgenroth, 

 and the author also experimented with the serum 

 resulting from treatment with chicken egg albumin, 



