152 Papers from the Department of Marine Biology. 



other hand, the weak alkalies penetrate without affecting the surface, 

 without killing the cell, and before functional activity is appreciably 

 affected. The easily penetrating group of alkalies are also lipoid 

 soluble and active in lowering the surface tension of water. Data for 

 a quantitative comparison with lipoid solubility and capillary activity 

 are not available at present. 



On comparing the acids with the alkalies several facts of interest 

 appear. The acids form a series much more evenly graded in prop- 

 erties. Consequently, two classes of acids, easily penetrating and 

 difficultly penetrating, are not so easily recognized. The acids which 

 correspond to NH 4 OH and the amines, the lipoid-soluble acids, are 

 benzoic and salicylic with possibly valeric. The remaining acids all 

 meet a resistance at the living cell-surface (abolished on death of the 

 cell) which varies specifically with the acid. Once the pigment is 

 turned red orange by the acid, removal of the tissue to sea-water does 

 not reverse the color change. The tissue is also killed and the pigment 

 diffuses away. Since the testis epithelium is an inert tissue, i. e., 

 contains no cilia or other indicators of functional activity, the relation 

 between entrance of an acid and change in functional activity could not 

 be observed. 



With acids as with alkalies ability to penetrate the cell-surface 

 appears to determine the toxicity of the acid. I am inclined to think, 

 but can not be certain of this, that, as in the case of the strong alkalies, 

 the lipoid-insoluble acids must destroy the normal impermeability of 

 the cell-surface before they enter. The most toxic of the lipoid-insol- 

 uble acids would therefore be those which destroy the surface most 

 rapidly, and they would penetrate the cell most readily for this reason 

 also. Destruction of the cell-surface appears to depend largely on the 

 strength of the acid, i. e., its ability to combine with proteins of the 

 cell-surface, but in part also on some specific, as yet unrecognized, 

 peculiarity of the acid anion. 



A few remarks in regard to Traube's Haftdruck theory may not be 

 out of place. This theory depends essentially on the Gibbs-Thompson 

 principle that a substance tending to lower the surface tension of water 

 will collect in the surface. If a membrane is at the surface the sub- 

 stance will tend to pass the membrane, and always in the direction of 

 the solution with the greatest surface tension. Difference in surface 

 tension, " Oberflaschendruck" or "Haftdruck," determines the direc- 

 tion and velocity of osmosis. The more a substance lowers or increases 

 the surface tension of water the less or the greater is its Haftdruck, and 

 it will pass from regions of low to regions of high Haftdruck. 



Originally Traube claimed that the direction and velocity of passage 

 of a substance through a membrane were independent of the membrane 

 and depended entirely on the Haftdruck of the solution. Had this been 

 the case Traube's theory would have been of real value as a simple 



