242 PROTOPLASMIC ACTION AND NERVOUS ACTION 



solution;^ in this case different reaction-products might 

 be obtained from the same reaction-mixture under the 

 influence of different catalytic agents, differences of 

 adsorption having the same effect as differences of 

 solubihty. Selective adsorption and selective catalysis 

 would thus be referred to the same conditions, and both 

 referred ultimately to the same conditions as selective 

 solubility. At present there is an increasing tendency 

 to regard both solution and adsorption as special cases 

 of chemical combination. But although protoplasm 

 contains solvents in which it is conceivable that certain 

 reactions may proceed with increased velocities, it does 

 not seem probable that such considerations can explain 

 the high velocities of the biologically more important 

 reactions, such as the oxidation of sugar. Many facts, 

 especially the phenomena of irritability, show that the 

 conditions determining the increase of reaction-velocities 

 in protoplasm are of a special kind and that the factor 

 of organized structure is all-important. It is not 

 simply a case of transferring a substance from a solvent 

 in which its reaction-velocity is low to one in which it 

 is high. 



It has been pointed out by various authors that when 

 adsorption is highly selective, displacements of equi- 

 librium may occur; thus an adsorbent may change the 

 H-ion concentration of a solution. Such effects may 

 be attributed to the selective adsorption of ions (Freund- 

 lich) ;^ but, as we have seen, the distinction between the 

 adsorption of a substance and its chemical combination 

 with the surface molecules of the adsorbent cannot be 



^ Cf. Bredig, Ergehnisse der Physiol., I (1902), 211. 

 ' Cf. Freundlich, Kapillarchemie. 



