PROTOPLASMIC STRUCTURK 8l 



pound may be a factor in preventing physical and 

 chemical alteration in li\'ing protoplasm. Preventive 

 effects of this kind probably form a chief factor in 

 the anaesthetic action of surface-active compounds, as 

 well as in the protective action which they often ex- 

 hibit (against salt action, haemolysis, or mechanical in- 

 jury).' 



ADSORPTION AND DEPENDENT PHENOMENA IN 

 COLLOIDAL SYSTEMS 



In general, colloids of the suspensoid group are less 

 readily adsorbed than those of the emulsoid group, in 

 correspondence with the fact that the latter are usually 

 surface-active, the former not. For the same reason 

 the suspensoids do not usually act as emulsifying agents, 

 while many emulsoids are highly effective in this regard. 

 The distinction, however, is not absolute, since finely 

 divided insoluble substances of various kinds may 

 emulsify oils under certain conditions;^ what is essential 

 is that the material should collect and form a continuous 

 layer at the surface between the phases. 



As a rule proteins are surface-active; their solutions 

 have lower surface- tensions than pure water and they 

 are readily adsorbed. The conditions are, however, 

 complex; the degree of adsorption may \ary with the 

 same protein according to its state of subdivision (which 

 varies with the salt content) or according to the H-ion 

 concentration of the solution; the latter condition deter- 

 mines the proximity to the isoelectric point and hence 



^ See pp. 207 fl. 



^Cf. Bancroft, loc. cit.; Journal of Physical Chemistry, X\I 

 (1912), 475. 



