164 



PHYSIOLOGY 



PROPORTIONS HYDROLYSED IN 100 c.c. OF A 5 PER CENT. 

 SOLUTION OF LACTOSE 



AMOUNT OF SUGAR (LACTOSE) HYDROLYSED 



Moreover, if we take only the earlier stages of the ferment action, it is fpund 

 that, with small proportions of ferment, equal amounts of substrate are 

 changed in successive intervals of time until about 10 per cent, has been 

 hydrolysed. This is shown in the following Table : 



2 PER CENT. LACTOSE WITH 



Time 

 hour 



* n 



1 



2 hours 

 3 



LACTASE 



Amount hydrolysed 

 3.2 

 6.4 



. 9.6 



. 16.4 



20.8 



These results can be interpreted only by assuming that the first stage in 

 the reaction is a combination of ferment with substrate. It is only this 

 compound which represents the active mass of the molecules, i.e. the mole- 

 cules of substrate which are undergoing change. This compound, as soon as 

 it is formed, takes up water and breaks down, setting free the hydrolysed 

 substrate and the ferment, which is at once ready to combine with a further 

 portion of the substrate. In such a case the velocity of reaction must be 

 directly proportional to the amount of ferment, and the same absolute 

 quantity of substance will continue tx> be changed in succeeding units of 

 time. Supposing, for instance, we had a load of bricks at the bottom of a 

 hill which had to be transferred to the top, and five men to effect the trans- 

 ference. The rate of transference would be directly proportional to the 

 number of men employed ; we could double the rate by doubling the men. 



