142 E. E. FREE 



to external agents one may recall the experiments of Sziies^ 

 on the increases and decreases of permeability caused, respec- 

 tively, by hydrogen peroxide and by almninium salts, and the 

 well known work of Osterhout^ on the antagonistic effects of 

 sodium and calcium salts on the penetration of each other into 

 tissues of Laminaria. Instances of normal functional changes of 

 permeability are the increased permeability of muscle cells dur- 

 ing excitation'' and of egg cells after fertilization. All of these 

 changes, whether spontaneous or due to external agents, may be 

 reversible and without apparent injury to the life processes of 

 the cell. Other similar examples are noted in the recent summa- 

 ries of Hober^ and Bayliss. "" A further case which is apparently 

 an example of variable permeability is the fact that cells are 

 usually relatively impermeable to the salts, sugars and amino 

 acids which form the building materials of protoplasm. It is 

 reasonable to assume occasional changes of permeability such as 

 would permit these substances to enter more readily. 



It is very probable that the protoplasmic colloids are of the 

 emulsoid type, that is, that they consist of two (or more) liquid 

 phases. A number of simpler colloids of this type have two 

 liquid phases which differ in composition only in the relative 

 proportion of water and of the substance of the colloid.^ Thus 

 a gelatine sol is believed to consist of globules containing rela- 

 tively more gelatine, suspended in a medium which contains 

 relatively less gelatine. The medium may be thought of as 

 a more dilute gelatine solution; the globules as a more concen- 

 trated one. At greater total concentrations of gelatine this 

 condition may be reversed, the more dilute solution becoming 



4 Jahrb. wiss. Bot. 52: 269 (1913). 



^Science 36:350-352 (1912), Bot. Gaz. 59:242-253 (1915). 



6 McClendon, Amer. Jour. Physiol. 29: 302-305 (1912). 



^ Physikalische Chemie der Zelle und der Gewebe, fourth edition, 1914, espe- 

 cially chapters 8, 10 and 13. 



* Principles of General Physiology, 1915, chapters 5, 12 and 18. 



9 van Bemnelen, Zeits. Anorg. Chem. 18: 14-38 (1898), Hardy, Jour. Phys. 

 Chem. 4: 254-273 (1900); Garrett, Phil. Mag. (6) 6: 374-378 (1903); Freundlich, 

 Kapillarchemie, 1909, pp. 395-398; Hatschek, Introduction to Physics and Chem. 

 of Colloids, 1913, pp. 43, 46, 59; Scarpa, KoU. Zeits. 15:8-10 (1914), Bayliss, 

 loc. cit., pp. 96-99. 



