192 BreiddJd and Rather a : 



bitter pit, or normal, practically destroys diastase in one to three 

 days." 



But in the next paragraph it appears that 20 grms. of pounded 

 pulp were added to only 10 c.c. of 1% Taka diastase. No experi- 

 ments are quoted which are comparable with Greenwood and 

 Rothera's, in which 1 grm. of pounded pulp was used with 5 c.c. 

 •of a 5% malt diastase, and the emphatic contradiction is therefore 

 most unjustifiable. 



The second criticism is that the observed accelerating action on 

 malt diastase was not an acceleration, but only an apparent accele- 

 ration, due to an experimental pitfall. 



Owing to actions of tannic acid on starch solutions causing pre- 

 cipitation of the starch, and also to the influence of tannic acid 

 upon the starch iodine test employed. Greenwood and R other a are 

 assumed to have been misled into taking the digestion of the starch 

 as complete, when it really was still incomplete. 



Though convinced that a real acceleration of malt diastase had 

 been obtained with both normal apple tissue and bitter pit 

 material, and that the experimental technique employed excluded 

 the pitfalls suggested by Prof. Ewart, it was decided to carefully 

 investigate the criticism raised as to the action of tannic acid. 



Freely acknoAvledging full indebtedness to Professor Ewart for 

 bringing the tannic acid complications to our notice, we find that 

 such complications cannot be applied to refute the experimental 

 results of Greenwood and Rothera. 



Tn the first place, though the blue colour produced by starch 

 with a small amount of iodine can be destroyed by tannic acid, 

 the proportions of the reagents are quite different to those of the 

 experiments of Greenwood and Rothera, in which the maximum 

 tannic acid could not exceed .002% final concentration, and in 

 wliicli the iodine was always used in large excess. 



For, in following a starch digestion, it is <_ustoniarv to remove 

 1 drop of the starch solution, which is then mixed with 1 drop of 

 a 1% iodine solution, and the blue colour ])rodueed under such 

 conditions is uninfluenced by tannic acid in concentrations up 

 to 1%. 



Only when the (|uantity of tannic acid is large, and tlie iodine 

 vei-y little in amount, does the decolourising power of the tannic 

 acid become inqioitant. 



Then again, we find that Ewait is unfortunate in his second 

 point that tannic acid inhibits diastatic action by forming a com- 

 pound with starch wliirli is resistant to the ferment. 



