196 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



of starch, may be insufficient and even absolutely misleading. Therefore, for the positive 

 identification of any given kind of starch other methods of differentiation should be coupled 

 with the histological method. 



(2) That young grains and mature grains may show differences not only in their histo- 

 logical characteristics, but also in their chemical and other reactions. The young grain 

 serves as a nucleus for the deposition of starch during the development of the mature 

 grain, it lacks lamellar structure, it shows a higher phosphorus content, it is more resistant 

 to the actions of both dry and moist heat, it is more resistant to enzymes and dilute acids, 

 and it exhibits differences in behavior towards iodine and aniline dyes. Likewise, the 

 outer coat of the starch-grain shows differences from the inner part. 



(3) That the starches from different somxes, when subjected to the ordinary labora- 

 tory procedures of differential study, show no differences in elementary composition; 

 that different starches show different percentages of water, starch-substance, kinds of 

 starch-substance, digestible matter, fat, furfurol contents, protein, ash, etc. ; that unim- 

 portant differences may be observed in specific gravity and in heat values; that starches 

 differ in the degree of acidity, and that the reaction is variable in accordance with the 

 indicator, as, for instance, acid to phenolpthaleine, alkaline to methyl orange, and neutral 

 to rosolic acid, and that different starches may react differently with the same reagent; 

 that phosphates constitute a more or less important element in the digestibility of starches, 

 not only of themselves directly, but also in the neutralization of alkaline impurities. 



(4) That the color reactions of different starches, different grains of the same starch, 

 and different parts of the same starch-grain may not be the same. 



(5) That the different swelling reagents show not only quantitative and qualitative 

 differences in relation to different kinds of starches, and even to different grains of the same 

 starch, but also that some at least of these possess individual characters by which their 

 reactions may be distingiiished from those of others. 



(6) That the starches of different kinds show quite a range of temperature at which 

 gelatinization begins and at which it is complete, and that in a given specimen the larger 

 grains tend to gelatinize at lower temperatures than the smaller grains. 



(7) That the reactions in polarized light, without and with a selenite plate, may vary 

 markedly, not only in starches from different sources, but also in different grains and in 

 different aspects of the same grain. 



(8) That the starch-pastes and pseudo-solutions obtained from different starches are 

 not identical in their stiffness and in their ijenetrability in relation to fabrics; that the 

 stiffness of the paste is affected by the length of the period of boiling, a longer period 

 increasing the stiffness of the pastes of the certain starches, but decreasing it in others; and 

 that gelatinized starch tends to undergo re\-ersion, and therefore becomes less digestible. 



(9) That if uninjured starch-grains are subjected in vitro to the actions of enzymes 

 under strictly aseptic conditions, absolutely no digestion occurs; but if the grains be broken, 

 eroded, or cracked, etc., or if bacterial action is not prevented, a more or less rapid erosion 

 takes place, which is more or less peculiar to the kind of starch and corresponds with the 

 peculiarities of the erosion phenomena observed when the starch is in situ; that oxj'gen 

 may be necessary in the saccharification of starch, as has been indicated in enzymic and 

 bacterial processes. 



(10) That boiled starches, whatever their source, are of equal digestibility, yielding 

 quantitatively and qualitatively the same saccharine products, provided the conditions 

 of experiment are the same. Different starches may nevertheless have different values 

 as articles of diet, owing to the presence in some of unpalatable or other forms of contami- 

 nation. Corn starch, for instance, should be equally as good as the comparatively expen- 

 sive arrowroot, but potato starch, which is of equal digestibility, has a comparatively 

 low value because of its being or becoming unpalatable. 



