CHEMICAL CHANGES IN LIVING MATTER. FERMENTS 183 



in the filtrate from the precipitate can be determined the total amount 

 of protein which has undergone hydration in the sample under observa- 

 tion. Or the amount of albumoses and peptones present in each sample 

 may be estimated by the intensity of the biuret reaction which can 

 be obtained. This method, however, suffers from the drawback that 

 the albumoses and peptones, at any rate in the action of trypsin, are 

 formed merely as a stage in the process, and the intensity of the 

 reaction will first rise to a maximum and then gradually disappear. 

 A very convenient method is that employed by Henri and by Bayliss 

 in the investigation of the kinetics of tryptic action, namely, the 

 determination of the conductivity of the solution. In the disintegra- 

 tion of the molecule caused by the action of the ferment, there is a 

 continuous increase in the conductivity of the solution, and this increase 

 can be regarded as an index to the rate of change in the substances 

 undergoing disintegration. 



By such methods it has been found that, when the quantity of 

 ferment employed is very small in comparison with the substrate 

 (the substance acted upon), the amount of change in a given time is 

 proportional to the amount of ferment present, and is (within limits) 

 independent of the concentration of the substrate. This is well 

 shown by the two following Tables representing the action of lactase 

 upon lactose (E. F. Armstrong) : 



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

 SOLUTION OF LACTOSE 



AMOUNT OF SUGAR (LACTOSE) HYDROLYSED 



