Bitter Pit and Sensitivity/ to Poisons. 235 



<-olt>ui-k'ss. On a(l(liii<r excess of iodiia-. tlie lilue eolnur is jx-riiia- 

 lient. As the jii-ecipitattMl stairli is allowed to settle, tlie lifjuid 

 above <.Mves eoloiii- reactions with iodine veiv like those oecunin;.' 

 •during diastatic action, and in the piesence of tannic acid, a small 

 amount of starch is easily overlooked. This is prohahly the ex- 

 planation of tlie erroneous statement made hy Kothera and Green- 

 wood, in le^^ard to the accelerating actiini of contact with apple 

 pul]), on malt diastase. If (».") per cent, solutions of diastase and 

 tannic acid are mixed and liltered, the filtrate thi'ows down a 

 white coagiilum with stai'ch solution, which may still lie uiidis- 

 solveil, even after .'3 days. 



The retardation of amylolysis by tannin was first shown l)y 

 Payen, but the action has been considered to be due to the tannic 

 .acid precipitating the diastase. (Czapek, Biochemie. vol. 1, ]>. 

 344). The following experiments are given in full, since they show 

 the exact action of the tannic acid. Needless to say, before each 

 sample was taken, the liquid was shaken, so that any precipitated 

 jstarch Avas evenly distributed, and the proper amount of iodine 

 was used in eacli case. 



Tannic acid produces a bulky white precipitate, with ordi)iary 

 papain and pepsina pcuci, l)ut pure pancreatin and diastase re- 

 main clear, or shew only a slight cloudiness. By treatment with 

 alcohol, and wasliing active diastase can l)e recovered. Gallic acid 

 does not precipitate any of these ferments appreciably, if clear 

 solutions are used, and the amount of precipitate formed with 

 tannic acid appear to depend upon the amount of contamina- 

 tion with foreign coagulable proteids. The action of the tannic 

 .acid is f)n the starch rather than upon the diastase, and hence 

 gallic acid, which is a feebler starch coagulin, affects diastase action 

 less than tannic acid does. 



In the first experiment (A) 5 c.c. of unfiltered 1 per cent, diastase 

 -was added to each 5 c.c. of filtered 1 per cent, starch solution, and 

 .■5 c,c. of the solution of gallotannic acid to each mixture. In ex- 

 periment (B) filtered 1 per cent, diastase was used, and the tem- 

 perature kept between 26° and 28° C. Portions of each solution 

 were tested at regular intervals of time with iodine, the colour 

 sequence as the starch dissolves ))eing l)lue, violet, purple, brown, 

 yellow, the last being merely due to tlie iodine, and being given as 

 ni\. 



