VALUES OF METHODS IN THE DIFFERENTIATION OF STARCHES. 309 



THE CHEMICAL REAGENT METHOD. 



WTiile all of the chemical af^ents bring about a complete iiitermoleeular disorganiza- 

 tion of raw starch, gelatinizing the grains and causing the loss of optical activity, the differ- 

 ent starches and different grains of the same starch and different parts of the same grain 

 may show more or less marked differences in their reactions, or, in other words, in the man- 

 ner in which this disorganization is brought about ; moreover, each reagent exhibits certain 

 peculiarities of action which are more or less distinctive. In some starches the small grains 

 ai;e less resistant than the large, and in others the reverse; and some parts of the grains may 

 react very much sooner than others, as already stated. The i^rocesses with chromic acid are 

 in certain respects different from those of pyrogallic acid and the other chemical reagents ; 

 and those of chloral hydrate-iodine and ferric chloride differ from those of chromic acid, 

 pyrogallic acid, and Purdy's solution, as is instanced by those of the former being con- 

 spicuous by their concentration in the outer part of the grain, and those of the latter in 

 the inner part. With chromic acid the grain is broken down into a gelatinous capsule 

 and a semi-liquid contents, the capsule rupturing, the contents escaping and passing into 

 solution, and then the capsule disappearing. With no other of the reagents was this 

 observed, and there are other differences which are more or less marked and characteristic. 



Individualities in the reactions with chloral hydrate-iodine were observed in some 

 starches, as, for instance, in Triticwn, in which the grains become deeply colored, almost 

 black, and the intermolecular structure disorganized, but with relatively little swelling. 

 Great variations were recorded in the different starches in regard to the extent of swell- 

 ing and in the changes in the forms of the grains. With some starches the alterations are 

 so slight that the forms of the normal grains are retained after the completion of gelatin- 

 ization, while in others the swelling and distortion may be so great that the gelatinized 

 grains bear no resemblance to the originals. 



Moreover, the sequence of changes, and also the various characters of the processes, 

 vary in the starches of different kinds, in different grains of the same starch, and also to 

 some extent with different reagents. In some starches the reaction with a given agent 

 begins typically at the proximal end, or at the distal end, or at protuberances or angles, 

 or at disseminated spots. Such peculiarities are not without significance because they 

 are common to closely related starches, as, for instance, those of members of a given genus. 

 These differences are not explicable upon the basis of mere physical or physico-mechanical 

 conditions, because if they were the region of beginning reaction and the sequence of 

 reactions in any given kind of grain would be the same with all of the reagents. The very 

 fact of the selectivity of parts by each reagent, and the differences in the sequence of the 

 events shown by the different reagents in many cases, are unmistakable indications of 

 peculiarities due to specific relationships between each reagent and the specific stereo- 

 chemic form of starch, each reagent demonstrating by its peculiar behavior the lack of 

 homogeneity of the starch-grain itself, of different grains of the same starch, and of different 

 starches as regards the form or forms of the starch-substance present. Of course, it is to be 

 expected that v/hen any two or more agents exhibit common tendencies, there will be corre- 

 sponding propensities for the same or similar lines or sequences of reaction to be followed; 

 for instance, if chloral hydrate-iodine and ferric chloride attack the outer part of the grain 

 in preference to the inner, and if chromic acid, pyrogallic acid, and Purdy's solution would 

 likewise exhibit a greater affinity for the inner part there will be corresi^onding tenden- 

 cies in each gi'oup for similar lines or sequences of reaction. 



Reactions are recorded in a number of instances which at first sight may appear to 

 be aberrant or wide and irreconcilable departures from a given prototype that is exhibited 

 by closely relatetl genera, recognized groups of genera, or members of a given genus, etc. 

 Thus, the reaction-curves of all the representatives of the Graminacece {Zea, Andropogon, 

 Panicum, Oryza, Triticwn, Secale, Hordeum, Avena, and Arrhenatherum) closely correspond 



