THE PERMEABILITY OF CELLS 553 



indicator is affected. Were the relation of Na and NH4 reversed, 

 some probability for such an explanation might be found. The 

 evidence (p. 528) that combined NH4OH or NaOH albumen does 

 not affect neutral red even in solution, that chloroform has no 

 influence on the combining power of albumen for alkali, whereas 

 cells killed by chloroform become as readily permeable for NaOH 

 as for NH4OH is strong proof that permeability and not reaction 

 velocity is in reality the phenomenon studied. Robertson's ('10) 

 experiments on the solution of casein in alkalies indicate that 

 equal concentrations of Na, K, Li, and NH4 dissolve equally 

 w^ell. Even though the velocity of solution is mainly due to the 

 rate of wetting of the casein particles by the alkali, the analogy 

 is all the closer to diffusion into a cell and any marked differences 

 in NH4OH and NaOH should appear. 



Lastly, it must be pointed out that the rate of penetration is 

 not exactly inversely proporiional to the degree of dissociation. 

 Among the weak alkalies trimethyl amine is much less dissociated 

 than methyl amine yet enters Elodea less rapidly. 



Overton's study of the penetration of the weak organic bases 

 into Spirogyra cells as indicated by precipitation of a tannate 

 has brought out the relation which exists between lipoid solubility 

 and permeability. According to Overton, ammonia and i;he 

 amines with the exception of the quaternary ammonium bases 

 are lipoid soluble. The two classes into which we may divide 

 the alkalies in respect to their power of penetrating living cells 

 are just the classes into which we may divide the alkalies in corre- 

 spondence to Overton's h^/po hesis. Traube has shown however 

 that the lipoid solubility of a substance is also connected with 

 a lowering of the surface tension of water by that substance. It 

 is to this property that he refers the ready penetration of lipoid 

 soluble substances, in accordance with his theory of osmosis. 

 It is quite probable that the relations shown by the alkalies may 

 be brought into line with Traube's theory but I have no data on 

 the subject and cannot at present discuss the question. 



I also agree with Barratt that NaOH combines with certain 

 constituents of Paramoecium but would limit the combination 



