DIFFERENCES IN DECOMPOSITION PRODUCTS OF DIFFERENT STARCHES. 155 



part is the typical reaction of pure starch as universally understood, but the explanation 

 of the different reaction of the outer part might not be the same in accordance with vari- 

 able conceptions of starch components and decomposition products. If one assumed that 

 there exists an inchvidual body between starch and erythrodextrins which is intermediate 

 in character, and which possesses properties of both, the violet reaction can readily be 

 accounted for, and as a corollary the outer or capsule part of the grain might with sufficient 

 reason be regarded as a transitional non-starch substance. There is, howe\'er, no necessity 

 for the assumption of the existence of such an intermediate body, but there is sufficient 

 evidence to warrant the conclusion that such bodies as have been so described are modified 

 forms of starch or mixtures of starch and dextrin. The violet reaction might satisfactorily 

 be accounted for, as experimental observations have shown, and which is in accord with our 

 views of the processes and products in the synthesis and analysis of starch, upon the basis 

 of the presence of a small and variable amount of erythrodextrin in the outer coat. Ery- 

 throdextrin is, as far as we know, the nearest individual to starch, and it is a natural con- 

 clusion that, since the grain grows by external accretion, there may be present in the outer 

 layer variable amounts of erythrodextrin in the course of transition into starch. Erythro- 

 dextrin gives a red reaction with iodine, and starch a blue reaction, and a combination of 

 the two a purple, blue-violet, or red-violet, or intermediate gradations, in accordance with 

 the proportions of these substances. The difference in color reactions between the inner 

 and outer parts of the grain can not therefore of itself be taken to indicate any specific 

 difference in the composition of these parts. There are, however, a number of facts wliich 

 very strongly suggest constitutional differences, as, for instance, the differences in solubility, 

 the differences in the reactions to aniline and other coloring agents, and differences in the 

 degree of digestibility and in the products of digestion. 



When comminuted grains are macerated in water the inner part goes into pseudo- 

 solution, while the outer part remains undissolved in the form of suspended flakes, etc., 

 and when raw starch is subjected to the prolonged action of weak acid, etc., the inner part 

 is dissolved, leaving skeletons of the grains which from their polariscopic properties may 

 be totally unchanged. This difference in solubility is in accord with the phenomena 

 observed when the grains are subjected to moist heat, and it would seem that it can not 

 be due in the least to the contaminating erythrodextrin, which is certainly more soluble 

 than starch; nor is there evidence that it may be due to the presence of other substances. 

 Differences in the reactions with aniline and other coloring agents have been referred to 

 particularly on pages 55, 56, and 58 and will be considered further in Chapters IV and VI. 



Pottevin's experiments (pages 134 and 147) furnish strong evidence of differences in the 

 constitution of the starch-substance in different parts of the starch-grain. He found, as 

 already stated, that the denser external parts of the grain are less digestible than the less 

 dense inner parts, and that the dextrin yielded by them is different, the dextrin from the 

 outer part being more difficult to saccharify and yielding a very much lower percentage 

 of sugar under the same conditions of experiment, and in being insoluble in strong alcohol, 

 and also differing in the degree of diffusibility. Roux (see pages 4G, 1 12, and 149) recorded 

 that not only were reverted and normal starches different in the degree of digestibility 

 under the same conditions of experiment, but also that the dextrins of reverted 

 starch, in accord with Pottevin, are, unlike those from ordinary starch, freely soluble 

 in strong alcohol. (See on reverted starch, page 111.) Further evidence of differences 

 in constitution that are suggested by variations in digestibility, etc., will be found in 

 Chapter IV. 



Here it might be noted incidentally that in experiments by O'Sullivan it was found 

 that the percentages of dextrin and maltose yielded by potato starch do not correspond 

 with those from the starches of malt, barley, corn, and rice. It was shown, however, by 

 Ford and Guthrie (page 193) that the differences were due to errors of experunent. 



