4IO SCIENCE PROGRESS 



in addition, however, the former investigator found that the 

 lower concentration of amyl alcohol accelerates the action of 

 urease. This must be explained by the fact that the retarding 

 influence due to dispossession of surface is more than counter- 

 balanced by the increased dispersion. The work of the Arm- 

 strongs and of Benjamin and Horton (191 3) had already 

 led them to assert that beyond doubt enzyme action took place 

 entirely at the surface of colloidal particles suspended in a 

 solution of the hydrolyte and not between substances in true 

 solution. The value of this possession of large surface by 

 enzymes is seen when the phenomenon of adsorption is 

 considered. 



Adsorption. — Enzymes, like other colloids, are capable of 

 adsorbing on their surfaces various other substances which may 

 or may not be colloidal. In this process of adsorption the 

 eznyme enters into a peculiar physical combination with the 

 substrate as a result of the diminution of surface energy at 

 the interface between the particles concerned. The existence of 

 such adsorption compounds can readily be demonstrated by 

 the method devised by Bayliss (191 1). In this method when a 

 colloidal solution of aluminium hydroxide is added to a dialysed 

 solution of the free acid of congo red, the undissociated acid 

 is thrown as a blue precipitate with the hydroxide. In fact 

 the acid and base act together as an adsorption compound 

 but are not combined chemically. If the precipitate be sus- 

 pended in water and boiled, chemical combination readily takes 

 place and the characteristic new colour of the salt is evident. 

 Many other proofs could be given, but we need only concern 

 ourselves here with those which refer to enzymes. Thus it is 

 found that an enzyme may be protected from the effects of 

 heat by being adsorbed. This will be referred to further under 

 " Temperature." Or again, trypsin will pass through porce- 

 lain, but will not do so if in contact with a solution of 

 caseinogate. 



The exact factors which determine the occurrence of adsorp- 

 tion are, however, not clearly known. Like other colloids, 

 enzymes are electrically charged. The importance of this 

 factor has been urged, but it is found that the kind of charge 

 possessed by enzymes may depend on their reaction, and whereas 

 it is but natural that adsorption may be facilitated between 

 colloids of opposite charges, it is difficult to understand why 

 adsorption should take place between colloids of the same 

 charge, or even uncharged. Further reference will be made to 

 this subject under " Electrolytes." Northrop (1919), on 

 finding that the optimum digestion for an enzyme corresponded 

 to the optimum ion concentration for the combination, sug- 

 gested that the enzyme combined with the ionised protein 



