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. aoe sro s dicierinted Less strongly dissociated 
dimethyl, ethyl, and ’ — ae 1 NH,OH 
ae and trimethyl amine. 
NOH CaOHs. Ba(OH)2, Sr(OH)z. a iam 
Penetration very slow. Penetration slow. Penetration very rapid. | Penetration very rapid. 
Least toxic. Less toxic. Most toxic. More toxic. 
Accelerate oxidation Accelerate oxidation | Accelerate oxidation 
least.! most.1 less.1 
Least efficient in causing Most efficient in causing | Less efficient in causing 
development.? development.? development.? 
Lipoid insoluble. Lipoid soluble. 
Capillary inactive.3 Capillary active. 
1Acceleration of rate of oxidation in unfertilized sea-urchin eggs. Loeb, Journ. Biol. Chem., 14, p. 357, 1913. 
tilieution, p. 149 on fate and teers es Urs gC a Loeb, Artificial Parthenogenesis and Fer- 
3j. e., do not lower the surface tension of water. 
Two subclasses may be distinguished under each class. If the alkali 
is a weak alkali, 2. 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). and 
Sr (OH), are more toxic than NaOH, KOH, Ca(OH)., and N(C.H;),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, 7. 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 
