SUMMARY OF THE MORE IMPORTANT LITERATURE UP TO 1872. 89 



practically ecjually; and that while there may be slight differences in the external layers 

 arising from the adhesion or infiltration of some traces of albumin, fat, or wax, such dif- 

 ferences mercl}' cause a longer or shorter delay of the action of the iodine or solvent. 

 Diu-ing this year Schwarz (Ann. d. Chem. u. Pharm., 1849, Lxx, 54) and FehUng (Ann. 

 d. Chem. u. Pharm., 1849, lxxii, 106) reported their determinations of the quantity of 

 starch present by reducing the starch to sugar by dilute sulphuric acid and finding the 

 amount of sugar by means of the copper test. 



Soluble and insoluble forms of starch were examined by Maschke (Jour. f. prakt. 

 Chemie, 1852, lvi, 400; 1854, lxx, 1). In studying the structures of starches by the effects 

 of heating (wheat starch was taken as a type), he records that the peripheral layer con- 

 sists of cellulose which is colored red or brown by iodine, while the inner part is colored 

 blue. Wheat starch was heated to 40, 50, 60, 70 and 100, and at each temperature 

 examined. At 40 the grains show rings in large numbers, alternating light and dark; 

 at 60 outUnes of small grains appear in the center of the large grains; at 70 cracks or 

 breaks are formed by swelling; at 100 the grains are irregular, each resembling a collapsed 

 bag. All of these phenomena, Maschke states, can be explained upon the assumption 

 that every starch-grain is composed of 3 to 5 vesicles of different size placed one within 

 the other, the starch ("amylon") being present between these in granular form. The 

 appearance and disappearance of so many rings he attributes to the swelling up of the 

 ring-like, separated, granular amylon; and he regards the 3 to 5 circles which finally 

 remain as the boundary envelopes of the vesicles which compose the grain. He be- 

 lieves he has proved the existence of such a structure by means of the action of iodine 

 and sulphuric acid. The internal part of the grain, he states, consists of a soluble and 

 an insoluble substance; and by evaporation the former is converted into the latter, but 

 by the use of soh-ents, such as potassium hydrate, or hot water, or alcohol and sulphuric 

 acid, or when subjected to dry temperature of 150, the insoluble substance is converted 

 into the soluble modification. The terms soluble starch and insoluble starch are used 

 by him only with reference to the behavior of the two modifications of starch towards 

 cold water. According to Maschke, the numerous light and dark rings which lie between 

 the concentric vesicles are probably due to the presence of different modifications of the 

 starch-substance, and the light rings are the insoluble modification of the starch which 

 is present in granules lying side by side, while the dark rings are of the soluble modifica- 

 tion in hquid form in which the light rings are embedded. 



Soluble starch was prepared by Bechamp (Compt. rend., 1854, xxxix, 653) by vari- 

 ous means, such as nitric, sulphuric, and acetic acids, and solutions of chloride of zinc 

 and potassium hydrate. The preparation thus obtained was found by Bechamp to differ 

 from dextrin in several characteristics, and also from natural starch, inasmuch as when 

 the solution is boiled to a syrup no cloudiness appeared. In a later article (Compt. rend., 

 1856, xui, 1210) he discusses in detail the process of changing natural starch into soluble 

 starch, and he looks upon the latter as a special substance which stands between starch 

 and dextrin. 



It was noticed by Criiger (Botanische Zeitvmg, 1854, xii, 41) that all parts of the 

 starch-grain during growth do not react in the same way with iodine. The outer layer 

 of the grain resting upon the plastid behaves, he states, differently from the mass of the 

 grain, this layer staining a yellow or dark brov^Ti (the same coloration assumed by the 

 protoplasm and clilorophyl), while the rest of the grain stains blue and also more readily 

 tlian the outer layer. He I'egards this outer laj-^er as a substance which is in the process 

 of becoming starch, but which as yet does not stain blue with iodine. Young grains stained 

 very slowly wdth iodine, and the blue color was comparatively less pronounced than in 

 mature grains. Small grains treated with iodine stained yellow with iodine or showed 

 no color reaction. Criiger does not undertake the determination of the nature of this 



