1913.] Processes Operative in Solutions and Enzyme Action. 567 



however, in presence of ammonia, the change is retarded, in presence of 

 carbonic acid it is much accelerated. 



A second point of importance to be noticed is the fact that the enzyme 

 has maximum activity in solutions which are only moderately concentrated 

 and that whilst dilution has but little effect, the rate of change becomes less ' 

 and less as the concentration is increased.* 



In no particular, therefore, is the change a " mass action effect," nor are 

 the departures such that it can be supposed that the change is primarily 

 " unimolecular " and subsequently varied owing to the occurrence of secondary 

 changes : it is doubtful, also, if it be necessarv to take the occurrence of 

 reversible effects into account except perhaps in concentrated solutions. 



[Note added July 30. — Bourquelot and Yardon's recent experiments! 

 entirely justify this conclusion. These observers have digested aqueous 

 solutions containing glucose and various proportions of methylic alcohol 

 with emulsin and have determined the amount of glucose which remained 

 unchanged when equilibrium was established. Their results are shown in 

 fig. 1, in which the ordinates indicate the amount of glucose unconverted 

 and the abscissae the percentage by weight of methylic alcohol in the solutions. 



XO 40 60 ' 80 100% 



Fig. 1. 



They have also shown that when solutions in 70-per-cent. methylic alcohol 

 of varying amounts of glucose are digested with emulsin, the amount of 

 glucoside formed increases proportionally to the glucose present up to 

 about 12 per cent, of this latter but in more concentrated solutions at a 

 diminishing rate : the proportion of combined glucose being 82 - 6 per cent. 



* E., XIX, p. 336. 



t 'Compt. Rend.,' 1913, vol. 156, pp. 957 and 1638. Cf. 'Ann. Chim. Phys.,' [8], 1913, 

 vol. 28, p. 145 ; ' Bull. Soc. Chim.,' 1913, Xo. 14, pp. i-xxvm. 



