CHEMICAL CHANGES IN LIVING MATTER. FERMENTS 163 



Various methods may be adopted for the study of the velocity of ferment 

 action. If, for instance, we are investigating the action of diastase upon 

 starch, we should take solutions of starch and of diastase of known concen- 

 trations, keep them in a water bath at 38C., and at a certain point add, 

 say, 20 c.c. of ferment solution to every 100 c.c. of the starch solution. 

 At periods of five or ten minutes after the addition had been made, 5 c.c. 

 of the mixture might be withdrawn by a pipette and at once run into boiling 

 Fehling's solution. The precipitated cuprous oxide would be dried and 

 weighed, and would give directly the amount of sugar formed by the action 

 of the ferment. After obtaining a series of data in this way, a curve could 

 be drawn, showing the amount of change of starch which had occurred 

 in each unit of time. In the case of the action of invertase on cane sugar 

 the investigation is still easier. Since the change from cane sugar to invert 

 sugar is accompanied by a change in the rotatory power of the solution 

 on polarised light, it is necessary only to put the mixture of ferment and 

 cane sugar into a polarimeter tube, which is kept at a constant temperature 

 by means of a water jacket, and read off at intervals of a few minutes the 

 change in the rotatory power of the solution. From this change can be 

 easily calculated the percentage of cane sugar still present, and therefore 

 the total amount which has been converted into fructose and glucose. 



In investigating the action of proteolytic ferments, as, e.g. that of trypsin 

 on caseinogen, samples are taken at five-minute intervals and run into 

 some substance such as trichloracetic acid, which will precipitate all the 

 unchanged protein, but will leave in solution the products of hydration 

 of the protein. From the amount of nitrogen in the filtrate from the precipi- 

 tate can be determined the total amount of protein which has undergone 

 hydration in the sample under observation. 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 in- 

 tensity of the reaction will first rise to a maximum and then gradually dis- 

 appear. 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 disintegration 

 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 disinte- 

 gration. 



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

 iployed is very small in comparison with the substrate (the substance 

 jted uon), the amount of change in a given time is proportional to the 

 lount of ferment present, and is (within limits) independent of the con- 

 itration of the substrate. This is well shown by the two following Tables 

 >resenting the action of lactase upon lactose (E. F- Armstrong) : 



