76 PROTOPLASMIC ACTION AND NERVOUS ACTION 



at the surface of the catalytic agent, but it appears 

 probable that other factors (electrical) also enter in 

 many cases of adsorption-catalysis (see below). 



In considering the case of protoplasmic systems, we 

 may regard adsorption as of importance in two chief 

 respects: (i) as an essential condition in the determina- 

 tion of structure (through the formation of the 

 adsorption-films of the protoplasmic emulsion and in 

 membrane structure in general), and (2) as a main 

 factor determining the character and velocity of the 

 chemical reactions; i.e., as influencing or controlling 

 cell-metabolism. 



It is well known that the adsorption of dissolved 

 substances of low molecular weight is, as a rule, a strictly 

 reversible process, with the equilibrium conditions 

 defined by the formula xjm = kcn , where x is the quantity 

 adsorbed, m the mass of the adsorbent, c the concentra- 

 tion of the substances in solution, and k and n constants. 

 On the other hand, in the case of colloidal substances or 

 other substances of high molecular weight, adsorption 

 frequently leads to a change of properties, the substances 

 becoming converted into relatively insoluble or resistant 

 varieties^ (possibly polymerized). In such cases the 

 process may be difficultly reversible or irreversible, a 

 fact of much interest as bearing on the question of the 

 conditions under which the more permanent portion 

 of the protoplasmic substratum is formed. In general, 

 organic growth appears to depend on the deposition of 

 relatively stable or persistent structural elements or 

 material in apposition to other elements or material of 



^ Cf. Hober, op, cit., p. 220, for instances of anomalous or irre- 

 versible adsorption. 



