THE STARCH-SUBSTANCE A NON-UNIT SUBSTANCE. 303 



the proximal end and sides persist after the distal end and inner part have broken down. In 

 the behavior of these two parts with iodine distinct differences are noted in both the inten- 

 sity and the color of the reactions. After gelatinization by boiling, and the addition of 

 iodine, if the grains arc intact, they are usually colored a light to a deep indigo-blue or a 

 bluish-violet. By further heating the capsules are ruptured and the semi-fluid contents, 

 which are colored an indigo-blue, partially or completely escape. Unless a decided excess 

 of iodine has been added, the capsules will be found to be colorless, sometimes containing 

 more or less of the blue-reacting starch, usually at the proximal end of the grain. By the 

 further addition of iodine the affinity of the blue-reacting starch for iodine is practically 

 satisfied, so that now the caiisules react and become colored, but ncAcr blue, generally some 

 tone of blue-red, ranging from a bluish-violet to a reddish- violet, heliotrope, and old-rose, 

 or a wine-color or rarely a yellow-brown or browTiish-red. Similar peculiarities are recorded 

 in the chloral hydrate-iodine reactions, in which of course the color reaction depends on 

 the presence of iodine. In the least resistant starch to the reagent the reaction is blue, 

 and as resistance is more and more marked in accordance with molecular peculiarities of 

 the different forms of starch, there is noted a corresponding and characteristic difference 

 in the color reaction, the most resistant yielding at first an old-rose or an ashes-of-rose, 

 deepening into a wine-color or a reddish-browTi coloration. 



At times in a given grain the progress of the reaction, together with the different de- 

 grees of resistance of the component starch-forms, can be followed and determined by the 

 differences and the changes in coloration, as, for instance, in the chloral hydrate-iodine 

 reaction with Mucuna, Lens, Lathyrus, Pisum, and many other starches. Gelatinized 

 starch is more sensitive to iodine than raw starch, and as far as known all boUed starches, 

 and starches gelatinized by chemical reagents, if the reagents do not interfere with the 

 iodine reactions, whatever their color reactions with iodine in a raw state, give a blue 

 reaction with iodine, with the single exception of grains like those of Alocasia putzeysi, 

 which normally give a wine-color or other color of reaction which is at present ordinarily 

 accepted as being peculiar to erythrodextrin and glycogen, but not to starch. 



It would seem from this, with the exception noted, that gelatinization, by whatever 

 means, by breaking up the intermolecular structure dissipates partially or completely 

 certain of the properties which serve to distinguish one form of starch from another. The 

 only part of the grain that is not thus reduced is the capsule, which represents but a small 

 fraction of the original weight of the grain. If these capsules are collected, repeatedly 

 washed by centrifugalization, boiled until completely disintegrated, and then tested with 

 iodine, the color-reaction will be found to correspond with that recorded in the intact 

 capsules. There is thus shown to be some marked molecular difference between the outer 

 and inner parts of the grains which is very persistent. It is doubtless in this intermolecular 

 disorganization of the starch-grain that is to be found the explanation of the identity in 

 the degree of digestibility of different starches, whatever the source, as shown on page 190. 



The so-called solution of starch is, as has been clearly pointed out in previous chapters, 

 a heterogeneous mixture; and, moreover, it is evident that such solutions prepared from 

 different starches are heterogeneous mixtures which differ from one another. It therefore 

 follows that differences in starches are owing not merely to peculiarities of intermolecular 

 arrangement, but also to peculiarities of intramolecular structure or molecular configuration. 



A striking and significant differentiation of the inner and outer parts of the starch- 

 grain is manifested in the reactions with the chemical reagents. Thus, in the reactions 

 with chloral hydrate-iodine and ferric chloride the outer part of the grain in almost every 

 starch is first to react and to be gelatinized, while with chromic acid, pyrogallic acid, and 

 Purdy's solution the inner part is usually the more sensitive. Again, different parts of the 

 surface of the grains and different internal parts may exhibit more or less marked differ- 

 ences in sensitivity. When secondary lamellae exist, they are usually affected before the 



