96 



CARBOHYDRATES. 



higher price. The markings are caused by the arrangement of 

 the material composing the granule in alternate layers of cellulose 

 and granulose. 



Quantity of Starch. The quantity of starch (percentage) in 

 the following food-plants is 



Sweet potato . 16.05 



Potato 20.00 



Beans 33.00 



Peas 49.30 



Wheat 57.88 



Oats 60.59 



Eye 64.65 



Indian corn 67.55 



Kice ...'.. 88.65 



The presence of starch is determined by the addition of a little 

 tincture of iodin, which gives a blue color. This reaction is due 



to the granulose, and not to the cel- 

 lulose. Starch cellulose differs in 

 some respects from ordinary cellu- 

 lose, as is demonstrated by its solu- 

 bility in some reagents which do not 

 dissolve the latter* 



Starch is insoluble in cold water. 

 When boiling water is added to it in 

 an amount twenty times its weight 

 the granules swell and burst, and 

 there is formed a gelatinous mass 

 which is called " starch-paste." This 

 paste will respond to the iodin test, 

 showing it to be, principally at least, 

 granulose. If the amount of water 

 added should be one hundred times the weight of the starch, a 

 solution of granulose is made, the insoluble cellulose falling to the 

 bottom of the vessel. This starch solution will likewise respond 

 to the iodin test. 



Amylodextrin (Soluble Starch, Amidulin). When starch-paste, 

 produced in the manner above described, is heated to a temperature 

 of 40 C. on a water-bath, and saliva is then added, the paste 

 changes from a gelatinous to a watery condition, and in this fluid 

 soluble starch now exists. This soluble starch gives also a blue 

 color with iodin. It filters readily, whereas starch-paste, even in 

 dilute solution, filters with difficulty. Soluble starch is dextro- 

 rotatory that is, it rotates the ray of polarized light to the right. 

 This substance is the first product of the conversion of starch into 

 sugar by saliva ; and if the action is not stopped, as it may be by 

 boiling, the stage of soluble starch is only a temporary one, it pass- 

 ing quickly into that of dextrin. As will be seen hereafter, the 

 ingredient of the saliva that changes starch into soluble starch is 



FIG. 83. Starch-grains. 



