INORGANIC SALTS 183 



solution are prevented in the presence of a lilllc CaCl,. 

 The toxic action of the pure solution and also its 

 membrane-forming action are correlated with a 

 permeability-increasing action, as in the other cases 

 cited above; and the correspondence with the bcha\iur 

 of the jelly seems to imply that the increase of permea- 

 bility in the pure solution is to be referred also to the 

 replacement of water-insoluble Ca compounds (e.g., 

 Ca proteinates or soaps), on which the properties of 

 the plasma membrane depend, by soluble Na compounds. 

 There is much independent evidence that this role 

 of calcium compounds — i.e., of determining the properties 

 of the surface layers of cells — is a general one; we may 

 thus understand the importance of Ca to all normal 

 cell-processes (stimulation, etc.) w^hich depend on changes 

 in the surface layers. The peculiar relation of Ca to 

 the coherence of blastomeres and of plant cells has 

 already been mentioned; according to the earlier work 

 of Mangin, Ca compounds (''Ca-pectate") in the middle 

 lamella of plant cells are essential to the structural 

 coherence of cellular tissues; when the Ca is replaced 

 by Na, the cells tend to fall apart. Similar phenomena 

 are also well known in the epithelial tissues of animals; 

 e.g., in the ciliated epithelium of Mitylus the cells swell 

 and fall apart in pure solutions of many Na and K salts, 

 and this effect is prevented by Ca.' Recently the 

 changes occurring in plant tissues in pure NaCl solutions 

 have been studied in much detail by Hansteen.^ The 



^ R. S. Lillie, American Journal of Physiology, XVII (1906), 89; cf. 

 p. 122. 



^Hansteen (Hansteen-Cranner), Jahrh. wiss. Botanik, XIA'II 

 (1910), 374; LIII (1913-14), 536; Bcr. dcutsch. Bolan. Gcs., XXXVII 

 (1919), 380. Also his recent book, Zur Biochemic u. Physiologic dcr 

 Grenzschichten lebender Pflanzenzellen, Kristiania (1922). 



