112 PROTOPLASMIC ACTION AND NERVOUS ACTION 



tion in balanced solutions, a fact corresponding to the 

 lipoid-insolubility of these compounds. In pure solutions 

 (pure NaCl solution) the salts alter the properties of the 

 plasma membranes and secondarily may penetrate;^ 

 but this fact is in no way inconsistent with Overton's 

 view, which applies to the unaltered membrane. A 

 definite correlation between lipoid-solubility and power 

 of penetrating the living plasma membrane may be 

 said to have been established by Overton's work and 

 succeeding studies of the same kind; and this generaliza- 

 tion is an important one, since it indicates (as do many 

 other facts) that the lipoids play an essential part, 

 apparently in association with the other chief colloidal 

 compounds of protoplasm, the proteins, in the formation 

 of membranes and probably of the other solid structural 

 elements of cells. 



Three chief methods have been employed in determin- 

 ing the permeability of cells to dissolved substances: 

 (i) the plasmolytic or osmotic method,^ (2) the partition 

 method,^ and (3) the electrical conductivity method.'* 

 To these may be added methods dependent on the use 

 of indicators, either those normally present in cells,^ 



^ Cf. Osterhout, Science, XXXIV (191 1), 187. 



2 Overton, Arch. ges. Physiol., XCII (1902), 115. 



3 Hedin, Arch. ges. Physiol., LXVIII (1897), 229. 



4Tangl and Bugarszky, Zentr. Physiol., XI (1897), 297; G. N. 

 Stewart, ibid., p. 332; Osterhout, Science, XXXV (191 2), 112, and 

 later papers; also Osterhout's recent book, Injury, Recovery and Death 

 in Relation to Conductivity and Permeability, Philadelphia, 1922. 



s Harvey, Internal. Z. physik.-chem. Biol., 1 (1914), 463; Crozier, 

 Journal of Biological Chemistry, XXIV (1916), 255, and Jour. Gen. 

 Physiol., IV (1922), 723; Haas, Journal of Biological Chemistry, XXVII 

 (1916), 225. Cf. also Jacobs, American Journal of Physiology, LIII 

 (1920), 457. 



