232 PROTOPLASMIC ACTION AND NERVOUS ACTION 



divided suspensions of water-insoluble materials (chalk, 

 Ca-phosphate, etc.). 



In his textbook^ Hober has described various other 

 instances of protective action and has discussed briefly 

 the general biological significance of this phenomenon. 

 In Hving organisms, where water-insoluble materials 

 constitute an indispensable element in the formation of all 

 permanent structure, protective action is of great impor- 

 tance. Many otherwise insoluble materials are thus 

 kept in a permanent state of fine dispersion or pseudo- 

 solution. It is well known that uric acid and cholesterol 

 are present in serum in concentrations far higher than 

 correspond to their solubiKty in water; presumably 

 they are held in suspension as ultra-microscopic particles 

 by the protective action of the serum proteins. Pauli 

 and Samec^ have shown that gelatine, serum albumin, 

 and other proteins may keep large quantities of insoluble 

 calcium salts (sulphate, phosphate, carbonate) in appar- 

 ent solution. The silver salts in photographic plates 

 and the Ca-phosphate in milk are other instances of 

 insoluble materials kept in fine dispersion by protective 

 colloids. The suggestion has been made that the forma- 

 tion of pathological concretions in higher animals 

 (gallstones, uric acid deposits) is an expression of defi- 

 ciency in protective colloids. It is probable that in the 

 formation of normal structures, such as bone, by sepa- 

 ration of insoluble salts as a finely divided and struc- 

 turally regular deposit, the protective action of the proto- 

 plasmic colloids is a necessary factor; presumably in 

 the absence of this factor the particles would be flocked 



' Page 344. 



2 Biochem. Z., XVII (1909), 235. 



