A NUTRITIVE CARBO-HYDRATE 663 



of carbo-hydrates, chiefly starch, which receives the special 

 title of amylum, 10 of proteids, with water, and ash. Oat- 

 meal contains 63 of starch and about 12*6 of proteids, with 

 traces of a bitter amorphous alkaloid ; barley, 64 starch, 

 12 proteids ; rice, 83 starch, 5 proteids ; potatoes, 21 starch, 

 2* 8 proteids. From any of these sources pure starch is 

 got by fine division of the grain or root ; sometimes facili- 

 tating separation of other plant constituents by fermenting ; 

 washing the starch granules from fibrous matters, straining, 

 and drying. The white starch used for medicinal and 

 dietetic purposes is dried in powder or granules. The 

 blue preferred for the laundry is in blocks, splits as it 

 dries into columnar masses, is coloured by addition of a 

 little indigo, and generally contains about 18 per cent, 

 of water. 



Arrowroot is the starch of the Maranta arundinacea ; 

 sago, the granular starch from the sago palm ; tous-les- 

 mois, the large ovular granules from the rhizomes of several 

 species of Canna ; tapioca or cassava is prepared from the 

 expressed juice of the roots of Manihot utilissima. Corn 

 flour or Oswego is the flour of Indian corn deprived of 

 gluten by a weak solution of soda. 



Starch consists of round or oval granules comprising a 

 cell- wall enclosing concentric layers of granulose. The large 

 grains from potatoes are about g^^th of an inch in their 

 long diameter, the small rounded grains of rice measure 

 aDTTo^ 1 ^ an inch. Starch grains from various sources differ 

 in appearance when examined under the microscope. 

 Wheat starch presents a mixture of large and small granules, 

 which are lenticular in form, and marked with faint con- 

 centric striae surrounding a nearly central hilum. The 

 maize granules are more uniform in size, frequently poly- 

 gonal, smaller than those of wheat, having a very distinct 

 hilum, but without evident concentric striae. Rice granules 

 are extremely minute, and nearly uniform in size, polygonal, 

 the hilum small and without striae (B.P.). 



Starch is insoluble in cold water, has the specific gravity 

 1*5, and hence is deposited when mixed with water. The 

 cell-wall consisting of cellulose and the contained granulose 

 are isomeric, having the formula usually given as (C 6 H 10 5 )x. 



