200 



Scientific Proceedings (76). 



melanophore we are dealing with a modified and disguised type 

 of smooth muscle cell. 



114 (1178) 



Characteristics of the precipitation reaction. 



By Richard Weil. 



[From the Department of Experimental Medicine, Cornell Medical 

 College, New York City.] 



In a previous communication I showed that when a chemically 

 pure protein, such as crystallized egg albumin, is used as antigen, 

 it combines with the precipitin of immune serum to the complete 

 exhaustion of either factor from the mixture. From these ob- 

 servations the conclusion was drawn that an equilibrium subject 

 to the laws of mass action, such as had been previously described 

 in precipitation reactions, does not exist in these reactions, those 

 results being attributable to the use of impure antigens, such as 

 complex native sera. Further study has shown that chemically 

 pure antigen unites with the precipitin in proportions that are 

 definite and constant. The same amount of precipitinogen 

 always "binds" an equivalent amount of precipitin, regardless of 

 the relative excess of the latter substance in the mixture. The 

 reverse of this statement likewise holds true. Hence it follows 

 that it has not been possible to demonstrate the Danyz-Dungern 

 phenomenon in the precipitation reaction when carried on with 

 pure reagents. It appears likely, therefore, that the reaction 

 conforms to the type of quantitative chemical reactions, and is 

 not comparable to the adsorption phenomena exhibited by mutu- 

 ally precipitating colloids. 



