80 EXPERIMENTAL OBSERVATIONS ON 



therefore the effect of the tendency to reversion in decreasing the 

 velocity of reaction in the late stages can be neglected. 



The same causes which produce the actual reversibility seen 

 in the case of strong solutions must be present in dilute solutions, 

 and emphasis must be laid upon the fact that, on either side of 

 the equilibrium point for some distance, the tendency for the 

 reaction to run in the opposed direction must be present and ever- 

 increasing in amount as the equilibrium point is neared, so as to 

 stop the reaction at the equilibrium point. Hence before the 

 equilibrium point is reached there must be a decrease in velocity 

 due to the tendency to reversion. 



Accordingly it is not safe to assume that because a reaction 

 runs to 99 per cent, and over before equilibrium is reached, and 

 is therefore regarded as a complete reaction, that it will run up 

 to 99 per cent, with the same velocity as if there were no equi- 

 librium point and no tendency to reverse near the end-point. 1 



As pointed out above, Bayliss has shown that there is a ten- 

 dency, at least, to reversion in the case of caseinogen and trypsin ; 

 actual reversion has been shown with other enzymes : and even 

 in the case of the action of acids upon disaccharides, E. F. 

 Armstrong and R. J. Caldwell have demonstrated that there is 

 a tendency to reversal indicated by the rotation of the plane 

 of polarised light beyond the maximum value corresponding to 

 complete hydrolysis. 



In fact, the retardation due to products of reaction which 

 causes the velocity in the later stages to fall off from the loga- 

 rithmic expression may in all cases probably be ascribed to the 

 tendency to reversion. The usual view that the drop is due to 

 removal of enzyme from the sphere of action by its combination 

 with one or more of the products of reaction is not incompatible 

 with this supposition. For just as it is supposed that, in order 

 that the action may proceed from left to right, it is necessary for 

 the enzyme to enter into some relationship or combination with 



1 Visser (quoted by Hamburger, Osm. Druck und lonenlehre, vol. iii. p. 97, 

 1904) found that the action of invertase upon cane-sugar was nob quite 

 complete, as always 1 per cent, of the cane-sugar was left. Visser deduced 

 a formula which gave a constant with his own results and those of Henri. In 

 this he first, as recommended above in the text, retained the reversibility expres- 

 sion; and secondly, introduced a variable for the alteration in intensity of action 

 of the enzyme throughout the reaction. The method suggested in the text for 

 making the second of these two corrections is different from that of Visser. 



