70 EXPERIMENTAL OBSERVATIONS ON 



according to Henri, the equilibrium constants for the compounds 

 between the enzyme and the two bodies to which it is united are 

 the other way round in relative magnitude (m = 40, and ^=120); 

 and on taking these the value of the constant does not decrease 

 but varies slightly around a mean value. For amylose acting upon 

 starch, where the logarithmic law is followed, 1 according to Henri, 

 the value of m and n are equal. It must be admitted that this 

 ingenious hypothesis and formula of Henri's are capable of explain- 

 ing the deviations on both sides from the logarithmic law ; but they 

 do not furnish an explanation of the experimental observations of 

 E. R. Armstrong, 2 to be described later, that there is first a linear 

 period, then a period when the velocity constant calculated by the 

 simple logarithmic formula increases, and finally a period when the 

 constant decreases. 



An interesting difference in action between diastase of malt 

 and the pancreatic juice obtained by the action of secretin is 

 noted by Henri. It has usually been stated that the same total 

 amount of starch is hydrolysed by diastatic enzymes in the same 

 time independently of the concentration of starch in the solution ; 

 but Henri found that this only holds for more concentrated solu- 

 tions of starch, and the limit at which the velocity of hydrolysis 

 becomes constant varies in the case of the different diastases. 

 Thus, in the case of diastase of malt, the quantity hydrolysed 

 increases with the concentration of the starch solution until a 

 strength of O75 per cent, has been reached, after which the 

 amount hydrolysed in a given time becomes constant ; while in 

 the case of the amylose of the pancreatic juice the maximum 

 conversion is not reached until the concentration passes 2 per 

 cent. The result may be due either to a greater concentration 

 of enzyme in the pancreatic juice, or more probably to a more 

 powerful enzyme. 



Variation in the concentration of cane-sugar in the case of 

 invertase gave the result that in dilute solutions the velocity 

 increased with the dilution ; in solutions of intermediate strength 

 (3-6 to 18 per cent.) 3 the velocity is independent of the concentra- 

 tion ; while in more concentrated solutions the velocity actually 



1 See, however, Horace Brown and Glendinning. 



2 Armstrong points out that a similar effect is seen in the measurements by 

 Horace Brown and Glendinning. 



3 That is, O'l to 0'5 normal in cane-sugar. 



