PROD UCTS OF DIGESTION OF STARCH. 395 



well-differentiated substances have been described. The first step in 

 the action is, according to all observers, 1 the formation of soluble starch 

 (amigdulin, amidulin, arnidogen, or amylodextrin). This substance is 

 rapidly formed, usually in one or two minutes ; it gives the same blue 

 reaction with iodine as raw starch or starch paste, and is precipitated by 

 tannic acid, by which it is distinguished from the dextrins formed in the 

 subsequent stages. 



In the second stage, this' soluble starch is decomposed into a sub- 

 stance giving a red colour with iodine and maltose. The substance 

 giving the red colour now gets the name given by Briicke of erythro- 

 dextrin; it corresponds to Nasse's dextrin, Griessmayer's dextrin-1 

 and Bondonneau's dextrin-a. 



In the third stage, this erythrodextrin is split up into a dextrin (or 

 several dextrins), giving no coloration with iodine, and hence called 

 achroodextrin, and a further quantity of maltose. Finally, according to 

 some, a part of this achroodextrin breaks up, yielding more maltose, 

 and a variety of achroodextrin, altogether unaffected by diastatic 

 ferments, which with the maltose split off at different stages from the 

 intermediate products, forms the final product of the reaction, no matter 

 how long prolonged. 



These successive changes may be represented as in the following 



scheme : 



Starch 



Soluble Starch. 



I 



Erythrodextrin Maltose 



I 



Achroodextrin Maltose 



All observers are agreed as to the existence of soluble starch, and 

 practically all as to that of erythrodextrin, although Musculus and Meyer 2 

 state that, on carefully mixing dextrin stained with iodine, with soluble 

 starch stained with iodine, they obtained the colour of erythrodextrin, and 

 conclude that Avhat has been called erythrodextrin is probably such a mixed 

 colour. This result has not been confirmed by other observers ; still it 

 should be borne in mind that a pure substance has not yet been isolated, and 

 that at present erythrodextrin is only a name given to a substance supposed 

 to exist, because of a red colour which is obtained at a certain stage in the 

 digestion of starch by diastatic enzymes. The material which is found later 

 in the process, which is not a sugar and gives no coloration with iodine, has 

 been called achroodextrin, but it has none of the constant properties of a 

 pure simple substance, and is probably a mixture of several substances 

 (achroodextrins), though as yet none of these have been properly isolated. 



Musculus and Gruber, 3 working on starch solutions with dilute acids and 

 with diastase, differentiated, according to varying conditions of temperature, 

 amount of diastase added, and length of time of action of the ferment, three 

 achroodextrins (a, (3, and y), possessing, according to these observers, different 



1 Nasse, Arch. f. d. ges. PhysioL, Bonn, 1877, Bd. xiv. S. 474 ; Griessmayer, Chem. 

 Centr.-BL, Leipzig, 1871, S. 636; Briicke, " Vorlesungen," and Sitzungsb. d. k. Akad. d. 

 Wissensch., Wien, 1872, Abtli. 3; Bondonnean, Compt. rend. Acad. d. Se., Paris, 1875, 

 tome Ixxxi. pp. 972, 1210; Musculus, Ztschr. f.physiol. Chem., Strassburg, 1878, Bd. ii. 

 S. 177. 



2 Ztschr. f. physiol. Chem., Strassburg, 1880, Bd. iv. S. 451. 



3 Ibid., 1878, Bd. ii. S. 177. 



