The Permeability of Cells for Acids. 



151 



compounds most soluble in lipoid penetrate most readily. This can 

 only mean that more than one variable is concerned in determining 

 the rate of penetration of an acid. Before discussing the second vari- 

 able involved let us consider the facts in regard to the penetration of 

 the alkalies. Note also from table 2 that the series for adsorption by 

 silk is somewhat similar to the series for penetration rate. 



Table 4 summarizes the effect of alkalies, and indicates their division 

 into two very distinct classes, the strong and the weak. The strong 

 always meet a marked resistance at the cell-surface; the weak meet with 

 absolutely none and enter the cell instantly. Ability to penetrate the 

 cell determines the toxicity of the alkali. Hence the anomalous fact 

 that the weak alkalies are most toxic. 



TABLE 4. 



Strongly dissociated inorganic hydroxides, including 

 tetraethyl-ammonium hydroxide. 



N(C2H S )OH, NaOH, 

 KOH, Ca(OH) 2 . 



Ba(OH) 2 , 8r(OH)j. 



alkalis mpthvl ! Less strongly dissociated 

 dimeStlWrand ' ' k alkalies. NH 4 OH 



propyl amines. 



and trimethyl ainine. 



Penetration very slow. 



Least toxic. 



Accelerate oxidation 



least. 1 



Least efficient in causing 

 development. 2 



Lipoid insoluble. 

 Cap'llary inactive. 3 



Penetration slow. 

 Less toxic. 



Penetration very rapid. 



Most toxic. 



Accelerate oxidation 



most. 1 

 Most efficient in causing 



development. 2 



Lipoid soluble. 

 Capillary active. 



Penetration very rapid. 



More toxic. 



Accelerate oxidation 



less. 1 

 Less efficient in causing 



development. '- 



'Acceleration of rate of oxidation in unfertilized sea-urchin eggs. Loeb, Journ. Biol. Chein., 14, p. 357, 1913. 

 "Efficiency in artificial parthenogenesis of the sea-urchin egg. Loeb, Artificial Parthenogenesis and Fer- 

 tilization, p. 149, 1913, and Journ. Exp. Zool., 13, p. 577, 1912. 

 *t. e., do not lower the surface tension of water. 



Two subclasses may be distinguished under each class. If the alkali 

 is a weak alkali, i. e., belongs to the class readily penetrating, it will be 

 more toxic the more highly dissociated it is. If the alkali belongs to the 

 class of strong non-penetrating alkalies its toxicity will depend on the 

 specific nature of the cation just as in the case of a salt. Ba(OH) 2 and 

 Sr (OH) 2 are more toxic than NaOH, KOH, Ca(OH) 2 ,and N(C 2 H 5 ) 4 OH. 



As shown by Loeb, efficiency in causing artificial parthenogenesis 

 of the sea-urchin egg and in accelerating the oxidations in the unfer- 

 tilized sea-urchin's egg run parallel with toxicity, i. e., penetrability is 

 a determining factor and degree of dissociation a secondary one. 



Finally the difference between the two classes of alkalies is so 

 marked that it seems better to speak of a resistance rather than a 

 permeability of the cell-surface for the strong alkalies. The normal 

 high resistance of the cell surface must then be altered by the alkali 

 before it can enter the cell. Consequently we find that once a strong 

 alkali has entered a cell, the cell is irreversibly injured, is, in fact, killed. 

 Many functional activities of a cell (for instance ciliary movement or 

 muscle contraction) cease before the strong alkali can enter. On the 



