33O RALPH S. LILLIE. 



solved compound. Hence substances having a high degree of 

 surface-activity are as a class readily adsorbed. The effect is 

 the same as if a relatively slight coherence existed between the 

 solvent and the dissolved substance. Hence Traube conceives 

 of a surface-active substance as one in which the union or adhesion 

 between solute and solvent is slight; i. e., relatively little work 

 is required to separate the substance from solution; and he has 

 introduced the expression "Haftdruck" (adhesion-tension or 

 solution-affinity) to designate this condition. The capillary 

 activity of any substance in a given solvent varies inversely 

 with its solution-affinity (Haftdruck) relatively to that solvent. 

 The lower the solution-affinity relatively to water the greater is 

 the tendency of any substance to pass out of its solution in water; 

 this tendency favors the entrance of capillary-active substances 

 into other adjoining solvents or media, e. g., into and through 

 the membranes bounding cells. 1 The ready penetration of such 

 substances into living cells is in fact referred by Traube not to 

 lipoid-solubility, but to low solution-affinity in relation to the 

 medium bathing the cell. A tendency to surface-condensation 

 or adsorption is a characteristic accompaniment of low solution- 

 affinity to water; the marked physiological activity shown by 

 surface-active substances as a class is a direct consequence of 

 this tendency. 



According to data already cited, the narcotic activity of organic 

 substances shows a parallelism with both capillary activity 



1 Traube's attempts to apply this conception to a general explanation of osmotic 

 phenomena are not convincing. The fact that lipoid-solubility varies in the same 

 direction as capillary activity makes the question difficult to decide by experiments 

 on living cells. But in the case of dead cells, as well as of more permeable partitions 

 like parchment paper or collodion, surface-active and surface-inactive substances 

 appear to penetrate with equal ease. The difference between the rate of penetra- 

 tion of dissolved lipoid-insoluble substances into living and into dead cells shows 

 that the permeability of the partition (/. e., relative resistance to diffusion) is the 

 deciding factor in their entrance. Furthermore, instances are well known where 

 the rate of penetration of a substance through an artificial partition varies directly 

 with its solubility in the material composing the partition. Flusin's experiments 

 with rubber membranes are a good instance of this. The diffusion of substances 

 through the surface-films bounding the cells implies a passage either through or 

 between the membrane-constituents; and in the case of the living cell, solution of 

 lipoid-soluble substances ill the lipoids of the membrane is probably the main 

 factor in their entrance, although this entrance may be favored by adsorption due 

 to surface-activity. 



