The Permeability of Cells for Acids. 153 



explanation of how substances pass membranes and how they enter 

 cells, but unfortunately we know that the nature of the membrane 

 makes a great deal of difference in determining which substances can 

 pass it. Dead cells allow quite different substances to pass from those 

 which living cells do. Traube now admits that the Haftdruck of the 

 substance in the membrane is also essential. Surface tension is a 

 measure of the Haftdruck of a solution, but we have no method of 

 determining the Haftdruck of the substance in the membrane, so that 

 the simplicity of the Haftdruck theory is lost. Traube now states 

 that with certain substances even surface tension is no certain measure 

 of the Haftdruck of a solution, a condition which still further compli- 

 cates the theory (see Pfluger's Archiv, 153, p. 304, 1913). 



According to Traube the lowering of surface tension (capillary 

 activity), lipoid solubility, and osmotic velocity all run more or less 

 parallel, but osmotic velocity is dependent primarily on capillary 

 activity. Traube claims that capillary activity is a better measure of 

 narcotizing power than is lipoid solubility, but our data on this point 

 are rather scanty. The error in determining narcotic strength is large 

 and few accurate measurements of partition coefficients have been made. 



The Haftdruck of KOH is high. It slightly increases the surface 

 tension of water, whereas the surface tension of aqueous propylamine 

 is low. A normal solution of KOH has a surface tension (7 15) of 

 7.46 mg. mm. while n-propylamine = 4.63 and water = 7.3. 1 The pene- 

 trability of these two alkalies accords very nicely with the Haftdruck 

 theory. On the other hand NH 4 OH lowers the surface tension of 

 water very little despite the fact that it enters cells with great rapidity. 

 Thus in a capillary tube in which water will rise to a height of 91.5 mm. 

 n/4 NH 4 OH rises to 91 mm. while diethylamine rises to only 68.8 

 and piperidin to 67.5 mm. Yet NH 4 OH, piperidin, and diethylamine 

 all penetrate cells equally readily. 



My results with acids give no clue as to whether lipoid solubility or 

 capillary activity is the determining factor in penetration, since the 

 penetration series is not in exact agreement with either lipoid solubility or 

 capillary activity series. Wasteneys's results on the partition coefficients 

 between olive oil and water show that the " lipoid" studied does not 

 make very much difference. In any case butyric, propionic, and acetic 

 acids are most out of place in the penetration series. I had fully 

 expected them to penetrate the cells rather readily and was not a little 

 surprised to note their position. I at first thought that they were so 

 weak (only about 4 per cent dissociated) that the indicator (antedonin) 

 would not detect them. This assumption can not be true, however, 

 for valeric acid is also only 4 per cent dissociated, yet the indicator can 

 detect it readily enough. The only other possibility is that the indi- 

 cator is contained in some lipoid combination, similar in properties to 



'Surface tension figures from Traube. J. Ber. d. d. Physik ges., 10, p. 889, 1908. 



