PHENOMENA OF DIGESTIBILITY — BOILED STARCHES. 191 



become more digestible. According to Day, the raw starch-grains contain three substances 

 which, owinfr to their different color reactions with iodine, may be (Usiingiiished as blue- 

 ainijlosc, red-amylose, and rose-a7nylose. Blue-amylose is identical with the substance 

 known as granulosa or the i3-amylose of Meyer; red-amylose constitutes the outer layer 

 of the starch-grain and is more difficult of digestion than blue-amylose; rose-amylose 

 forms about 10 per cent of the inside of cereal starches, and is not found in potato, arrow- 

 root, tapioca, and sago starches, and is the least digestible of the three. Blue-amylose 

 constitutes the entire inside of potato, arro^\Toot, tapioca, and sago starches, and 90 per 

 cent or more of the inside of cereal starches, and is not rendered more digestible by boiling. 

 The digestibility of red-amylose is not increased by boiling, but rose-amylose is slowly 

 changed into blue-amylose by cooking and thus rendered more digestible. Day calls 

 attention to the fact that tlie skin formed in boiled starch contains reverted starch that 

 gives no color reaction with iodine, and which is very slow of digestion. Finally, starch- 

 paste made below the boiling temperature of water is as easily digested as that which has 

 been boiled for a few minutes. 



The use of impure gluten for the saccharification of starch, which dates back to Kirch- 

 hoff (1814) and Mathieu de Dombasle (1814), was resumed by Reychler (Ber. d. d. chem. 

 Gesellsch., 1889, xxii, 414), who made preparations of what he termed "artificial diastase." 

 These were prepared by means of dilute acids or acid salts (hydrochloric, phosphoric, acetic, 

 tartaric, and lactic acids, and acid sulphate of potassium, and acid phosphates of alkalies 

 were found most desirable). Well-washed, fresh gluten was subjected to the action of the 

 solvent at 30° to 40° for 4 to 5 hours. Reychler notes that the preparations of wheat flour act 

 like diastase, and that barley contains a diastatic constituent. In a number of experiments 

 with barley, wheat, and corn, the saccharifying action was found to be greatest in the case of 

 barley, and the intensity of action was increased by the addition of potato starch. 



Grierson (Pharm. Jour. Trans., 1892, xxiii, 187) subjected given amounts of boiled 

 starch, water, and pancreatic extract to a temperature of 37° to 38°, and determined 

 the period of the reaction with iodine to show the differences in the degrees of digesti- 

 bility of different starches. Corn starch yielded a blue reaction after 20 hours, antl wheat 

 and rice starch after 2 hours. Tapioca was colored a weak green after 30 minutes; but 

 tous-le-mois (from Canna cdiilis), Bermuda and St. Vincent arrowroots, and jwtato starch 

 showed no reaction with iodine after 19 minutes. Oat and wheat flour gave a starch reac- 

 tion after 80 minutes. He concludes that toxis-le-mois, arrowroots, and potato starch are 

 best for patients with weak digestions. 



A line of investigation similar to that followed by Grierson, but covering a somewhat 

 wder field, was pursued by Stone (The Carbohydrates of Wlieat, Maize, Flour, and Bread, 

 and the Action of Enzymic Ferments upon Starches of Different Origin, Bull. No. 34, Office 

 Expt. Sta. U. S. Dept. Agriculture, 1896), who carried out a plan to yield comparative 

 rather than absolute results. Care is stated to have been taken to secure identically the 

 same physical condition of all the starches, exposure under constant conditions of tempera- 

 ture and dilution, and to a uniform solution of diastase. As an index of the energy of the 

 action of the enzyme, a solution of iodine-iodide of potassium was employed, the test being 

 made by removing 0.5 c.c. of the starch preparation to a watch-glass or porcelain test-plate, and 

 adding a drop of iodine. When the blue reaction could no longer be obtained after repeated 

 tests the end of the experiment was recorded. Malt diastase, saUvary enzymes, pancreatic 

 enzymes, and Taka-diastase were used, together with potato, sweet potato, corn, rice, and 

 wheat starches. The main conclusions derived from his investigations are as follows: 



(1) The starches of sweet potato, maize, rice, and wheat vary greatly in their susceptibility 



to the action of enzymes. 



(2) This variation reaches such a degree that imdcr precisely the same conrlitions certain 



starches require 80 times as long as others for complete solution or saccharificatiou. 



