420 SCIENCE PROGRESS 



work on this subject has been done prior to the period under 

 review ; but BayUss in 19 19 pointed out that in dilute alkaline 

 solution the digestion of caseinogen by trypsin is slowed down 

 as a result of production of amino-acids which reduce the 

 hydroxidions in the solution. Also it is shown that when an 

 ester is hydrolysed by water the reaction becomes greatly 

 increased in velocity as the acid formed in the reaction accumu- 

 lates. Such results closely approximate to the phenomenon 

 to which Ostwald applied the term aiitocatalysis, but usually 

 this can be better applied in the case of enzymes to instances 

 in which the products of one reaction hasten the velocity of 

 another. Rockwood (19 16) found that amino-acids caused a 

 marked increase in the formation of reducing sugars by amylase 

 tested in salivary and pancreatic juice. In a continuation of 

 the work (191 7) he showed that glycine and protein also increase 

 the amylolytic activity of amylase. Partially hydrolysed pro- 

 teins also have an accelerating influence. He concluded this 

 was due to the amino radicle, not being exhibited by the salts 

 of the acids from which the amino-acids are derived nor by 

 acid amides. He showed also that at least one of the hydrogen 

 atoms could be replaced, but that the introduction of a sul- 

 phanitic radicle neutralised the effect. A similar acceleration 

 by certain amino-acids, such as glycine, glutamic acid and 

 alanine, on the activity of various amylases was also observed 

 by Ujihara (19 17), who found that the acceleration was often 

 as much as 45 per cent, to 100 per cent. 



Mathews (191 5) claimed that maltose and dextrose had an 

 inhibiting effect on ptyalin ; but this was not confirmed by the 

 work of McGuigan (19 19) already alluded to. 



Mention has also been made of the suggestion of Bancroft 

 (191 8) that products more highly adsorbed than the substrate 

 might dispossess the latter from surface. 



In some cases the products of the reaction precipitate the 

 enzyme from the solution, and it seems probable that this is 

 not due to any special combination between the enzyme and 

 product, but rather to some alteration of the colloidal state 

 of the enzyme or of the colloidal system with which the enzyme 

 is associated. 



Equilibrium. — ^As a rule, however, the reaction proceeds till 

 a state of equilibium is reached between products and substrate, 

 and the reaction stops, unless the products are removed by 

 absorption, as in nature or by dialysis. 



The phenomenon of equilibrium has been demonstrated by 

 many observers prior to 19 10. Bourquelot and Bridel (191 3) 

 showed that a true equilibrium existed in the case of /3-ethyl 

 glucoside and emulsin. This work was supported by that of 

 Bailly (191 7), who demonstrated that synthesis by emulsin of 



