18 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



graphic methods; and that the chief or essential primary proximate decomposition prod- 

 ucts, and conversely probably the essential final synthetic substances, are erythrodextrin, 

 aclu-oodextrin, maltose, and dextrose. 



VARIOUS VIEWS OF THE NATURE OF THE STARCH-SUBSTANCE, AND OF THE STRUCTURE, FORM, 

 AND MECHANISM OF FORMATION OF THE STARCH-GRAIN. 



Although starch was known to the ancients, as shown by the writings of Dioscorides, 

 our knowledge of this substance had its origin practically in the microscopical examina- 

 tion by Leeuwenhoek in 1716, by which he differentiated two fundamental structural 

 components. He found that when the grains were heated in water the inner part dis- 

 appeared, leaving nothing but the integuments (Hiillen); and that in the excrement of 

 birds that had fed on grain the same integuments could be found. From these observa- 

 tions he concluded that starch consists of a kernel or nucelus which is fit for nourishment 

 (nahrenden Substanz), and an outer, insoluble non-nutritive envelope. From this time 

 until the early part of the last century no material addition was made to the literature 

 of starch, at which period an era of research was initiated by VaqueUn (1811) and Islr- 

 choff (1811), the former finding that when starch is subjected to torrefaction it is converted 

 into a guinmy substance soluble in water; and the latter discovering that weak acid changes 

 starch into gum and sugar. The results of these investigations were confirmed by a num- 

 ber of contemporaneous experimenters. 



During the following twenty-five years, however, very little was added to our knowl- 

 edge apart from certain discoveries relating to the decomposition products and to the 

 agents which give rise to them. In 1819, De Saussure (Ann. de chim., 1819, xi, 379) 

 found that after setting raw starch aside for two years there were present a sort of paste 

 and sugar; a substance insoluble in cold water, but soluble in hot water, and giving a blue 

 reaction with iodine; and a body that was insoluble even in hot water, and which closely 

 resembled cellulose. To the substance soluble in hot water he gave the name amidine, and 

 to the cellulose-like body the name ligneux amylacec. 



Some years later Raspail (Ann. de sciences natur., Oct. et Nov. 1825, et Mars, 1826; 

 quoted by W. Nageli, Der Starkegruppe, Leipzig, 1874) reported that starch when heated 

 on a plate is converted in part into a sort of gum that is soluble in cold water, leaving a 

 residual insoluble sheath. The former stained blue with iodine, but the latter not. Ras- 

 pail's statement was at once disputed by Caventou (Ann. de chim., 1826, xxxi, 358), who 

 recorded that all parts of the grains stain blue with iodine; that raw starch does not con- 

 tain a substance that is soluble in cold water; and that when starch is subjected to dry 

 heat at 100° it is changed into a soluble substance resembling the amidine of De Saussure, 

 which substance he looked upon as a modified starch {amidon modific). 



It was then shown by Guibourt (Ann. de chim. et phys., 1829, xl, 183) that raw 

 starch does contain a substance that is soluble in cold water. He found that when starch- 

 grains have been conmiinuted in a mortar they are rendered partially soluble in cold water; 

 that this solution yields a blue reaction with iodine, and that upon drying it yields a resi- 

 due that is insoluble in cold water. The soluble substance he identified with the amidine 

 of De Saussure and the gum of Raspail, which latter, however, he holds is not a gum, as 

 stated by Raspail. He records that there is still another component (the integuments) 

 which stains blue with iodine, but is insoluble in cold water. 



Following Guibourt's article there appeared four contributions by Guerin-Varry 

 (Ann. de chim. et phys., 1834, lvi, 225, and lvii, 108; 1835, lx, 32; 1836, lxi, 66). In 

 the first of these Gu^rin-Varry states that starch consists of three substances: One (ami- 

 dine) that is soluble in cold water; another {aviidin soluble) that is insoluble in cold water 

 by itself, but which is held in solution by amidine; and an insoluble substance {amidine 

 teguvientaire) , the integuments or capsules of the grains. The amidin tegumentaire was 



