298 PHYSIOLOGY OF NUTRITION. 



3 cgr. of air-dry wheat starch in a watch-glass are added 3 c.c. of 

 concentrated malt extract, or 3 c.c. of an aqueous solution of the 

 ferment precipitated by alcohol. If we employ the latter we add 

 to it a very small quantity of Citric acid, since, as is shown in 113, 

 the presence of acid is very favourable to the activity of diastase. 

 The watch-glass is carefully covered, and we observe repeatedly 

 during twenty- four to forty-eight hours the changes which compara- 

 tively large starch grains undergo, drops of the fluid being placed on 

 the slide and examined microscopically. I satisfied myself that 

 there was a considerable difference in the behaviour of the starch 

 grains. Generally the corrosions produced have the appearance 

 represented in Fig. 109, a, 6, c, and d. The solution of the starch 

 substance proceeds from the outside inwards, and it forms bright 

 radiating bands which become broader with increasing corrosion, 

 and gradually the changes proceed further and further inwards, 

 the corrosion canals also frequently becoming branched, so that at 

 last the starch grain falls to pieces. 4 



1 See Detmer, Landwirtliscld. Jahrbiicher, Bd. 10. 



2 For further particulars see Wortmann, Botan. Zeituncj, 1890. 



3 The literature on the diastatic ferment has been very fully discussed by 

 Schleichert. See Nova Acta d. Leop.-Carol. Academ., Bd. 62. 



4 See Baranetzky, Die starkeumbildenden Fermente in den Pflanzen, 1878, p. 

 48. See also Krabbe, JaJirMcher f. ivissenschl. Botanik, Bd. 21. 



113. The Influence of Various Substances, and of Temperature 

 on the Transformation of Starch by Diastase. 



In each of a number of small glasses we place 25 c.c. of 1 per 

 cent, starch paste. The vessel a contains at first nothing further ; 

 to b are added a few drops of Hydrochloric acid ; to c a few drops 

 of a concentrated solution of Citric acid ; to d a few drops of potash 

 solution ; to e a few drops of alcohol ; to / a few drops o chloro- 

 form. Into each glass we now pour further 5 c.c. of malt extract, 

 and at the end of twenty-four hours add to each of the fluids, by 

 means of a glass rod, a small quantity of alcoholic Iodine solution. 

 The fluids a, e, and / do not colour blue. All the rest take on 

 a blue coloration on the addition of the Iodine. Alcohol and 

 chloroform have not arrested the action of the diastase ; the acids 

 and the potash, on the other hand, have rendered the ferment 

 inoperative. 



As regards the influence of acids in diastatic fermentation, it is, 



