310 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



in type excepting in the ferric chloride reactions of Triiiaim, Secale and Hordeurn, the 

 chloral hydrate-iodine reactions of Triticum and Hordeurn, and the Purdy's solution re- 

 action of Triticum. In a word, out of ten reactions in each starch all are in accord with 

 the Graminacete type excepting those noted in members of the tribe Hordecc, in which 

 there occur aberrant reactions as noted. Among individual members of a genus such 

 deviations are instanced in Maranta musaica, in which the reactions are in accord with 

 the Maranta type, except in the temperature and ferric chloride reactions, the former 

 being exceptionally high and the latter correspondingly low; and in Zingiber officinale, 

 in which the temperature reaction is comparatively exceedingly low and tlie ferric chloride 

 and Purdy's solution reactions very high. Such departures are at times obser\'ed in sub- 

 generic groups such as in Pisum and Brodicca. Thus, if we take the type of reaction- 

 curve of the genera constituting the group formed by Vicia, Phaseolus, Doliclios, Mucuna, 

 Lens, and Lathyrus as a basis of comparison (to which we will refer as the bean type), 

 it will be found in studying the records of Pisum that the reaction-curves of the mem- 

 bers of group 2, in which the starch-grains are histologically of the bean tj^pe, corre- 

 spond ciuite closely with the bean type of reaction-curve, and that on the other hand, the 

 curves of group 1, in which the grains are of a distinctly different type, show radical de- 

 partures, especially in the chloral hydrate-iodine, pyrogallic acid, ferric chloride, and 

 Purdy's solution reactions, exhibiting far greater sensitivity in the chloral hydrate-iodine, 

 ferric chloride, and Purdy's solution and strikingly less reactiveness in the pyi'ogallic acid 

 reactions. Like\vise in Brodicea is found a very high sensitivity of group 1 to p>'rogallic 

 acid as compared with groups 2 and 3 (see chart No. 198, page 615, Part II). Such aberrant 

 reactions may for the moment suggest unreliabilitj' of reaction-curves in expressing species 

 and generic specificities, but this is met by frequently recorded corresponding aberrations 

 from the typical that have been notetl by the botanist and zoologist, and by the pharma- 

 cologist and other specialists engaged in biological investigation, general and medical. In 

 fact, these discrepant phenomena may be merely seemingly and not actuallj^ aberrant. 

 As already repeatedly pointed out, slight stereochemic differences may cause more or less 

 marked variations in properties. 



Bearing upon an explanation of such aberrant reactions is a peculiar relationship 

 that has been recorded in these investigations between the reaclirity of a given starch and 

 the concentration of the reagent. A form of starch which reacts with extreme slowness 

 with a reagent of a standard strength may react with great rapidity if the reagent be some- 

 what diluted or concentrated. In other words, a definite relationship exists between the 

 molecular constitution of the particular form of starch and the concentration of the re- 

 agent, which relationship determines the rapidity of interaction, other things being equal. 

 Thus, in Triticum the molecule of starch has been so modified in its properties in relation 

 to chloral hydrate-iodine that it is feebly reactive with the standard strength of solution, but 

 very reactive with a slightly modified strength of solution, or, in other words, with a 

 solution of i^roper molecular concentration and relationship. Kabsch (p. 92) found with 

 some haloid salts that swelling may or may not occur depending upon the strength of 

 solution. A comparable condition was long ago observed in mixtures of variable proportions 

 of gasoline vapor and air, whicli in order to be explosive or to yield the maximum explosive 

 effect must be in percentages within definite limits; i.e., 1 volume of gasoline vapor to 16 

 of air, and 1 to 1, are not explosive, but all intermediate mixtures are, the greatest effect 

 being obtained when the mixture is in the proportion of about 1 to 9. In other words, 

 certain molecular conditions are requisite not only for reaction but also for different inten- 

 sities of reaction. It is probable that these seemingly aberrant reactions will be found to 

 be of considerable importance in the final analyses and comparisons of the peculiarities of 

 any given starch and its relatives, in bringing to light obscure molecular variations and their 

 causes, and especially in the diiferentiation of the stereoisomers. 



