New York AGRICULTURAL EXPERIMENT STATION. 27h 
presented, viewed in the light of our present knowledge regarding 
reactions having similar characteristics, have forced us to regard the 
action studied as a case of adsorption, with the formation of what 
van Bemmelen calls “ adsorption compounds,” that is, physical com- 
binations with composition varying continuously with the conditions. 
It must be confessed that much remains to be learned about ad- 
sorption compounds, and the phenomena of adsorption. They, how- 
ever, have certain characteristics in common, as summarized on p. 
262, and the possession of these characteristics by the reaction 
between dilute acids and casein, together with the complete failure 
of the reaction to agree with the accepted laws of chemical com- 
bination, lead us to classify the process as an adsorption. Whether 
other proteids also take up. acids by adsorption, or whether casein 
and silk are peculiar in this respect, it is useless to speculate about 
until careful quantitative tests have been made with other proteids. 
For an interesting speculation upon the possible biological sig- 
nificance of adsorption, the reader is referred to the discussion at 
the close of Freundlich’s recent paper.! 
Viewing the action between casein and acids as an adsorption 
practically brings us back to Hammarsten’s original proposition, in 
regarding the action as one not strictly chemical; though his con- 
clusion was based on results that could not be accepted as at all 
decisive, especially in view of the facts we now possess which were 
not then known. ; 
*Ztschr. Pivysik. Chem., 572385. 1906. 
