1919] 



MCGINTY — DIASTASE ACTIVITY OF SOLAN UM TUBEROSUM 245 



the last two a very small amount of starch was hydrolyzed after 

 24 hours. While the latter results must be considered positive, 

 the figures are so small as to be almost within the range of 

 experimental error. 



Since the activity of diastase is accelerated by small amounts 

 of acids, it was thought that the activating effect of the boiled 

 juice might possibly be due to its hydrogen ion concentration. 

 Accordingly, determinations were made in two cases which gave 

 an H ion concentration of P H 5.7 and P H 6.2. This very slight 

 acidity could hardly influence the activity of the enzyme. How- 

 ever, a solution consisting of mono- and dipotassium phosphate 

 having the same P H value was substituted for the boiled juice 

 in each case, but failed to have any activating effect. 



Another point of some interest in regard to diastase activity 

 was incidentally observed in the course of these experiments, 

 that is, the direct effect of the time factor upon diastatic activity 

 of potato juice. Doby and Bodnar (*15) report that when the 

 juice was preserved with toluol and allowed to stand in the dark 

 at 8-10° C. for 24 hours or longer, its diastatic activity increased. 

 As stated, the results reported here were obtained incidentally, 

 without any effort to provide Doby and Bodnar's conditions, and 

 are given for what they are worth (table in). The juice used 

 was preserved with 2 per cent toluol and stood at room tempera- 

 ture in partial light. 



TABLE III 



EFFECT OF THE TIME FACTOR UPON THE DIASTATIC ACTIVITY OF 



POTATO JUICE 



Sample 



Relative diastatic activity 



After standing 24 hrs. 



66 

 59 



These results indicate that under the conditions which ob- 

 tained in the experiment there is a marked decrease in the dia- 

 static activity of the potato juice on standing 24 hours. This is 

 directly opposed to the conclusions of Doby and Bodnar, who, 



