404 



STARCHES, GLANDS, &c. 



and in the majority of grains is near the broad end. The size of the 

 grain, the character and position of the hilum sufficiently distinguish 

 this starch from potato starch, which it otherwise resembles. 



Curcuma starch, from the rhizomes of C. angusti folia, Roxburgh, 

 and C. leucorhiza, Roxburgh (N.O. Scitaminece), is known as East 

 Indian arrowroot and is largely used in India, although it does not find 

 its way, to any great extent, to this country. 



The grains average about 36/z to 60//, in length, although both 

 larger and smaller ones may be found. They vary considerably in 

 shape, but typical ones are of an elongated ovate outline. The hilum 

 is situated in a little projection from the narrow end of the grain, and 

 is therefore remarkably eccentric ; it is often indistinct, but its position 

 can be found by following the concentric striae which are usually 



FIG. 224. Curcuma Starch. Magnified 300 

 diam. (Tschirch. ) 



discernible. The grains are nearly flat, appearing as rods when 

 viewed from the edge. 



Starch is a polysaccharose of the formula (C 6 H 10 5 ) n . Boiled 

 with water the grains swell, burst and partially dissolve, forming an 

 opalescent solution which, sufficiently concentrated, gelatinises on 

 cooling (starch paste). Infusion of malt or a solution of diastase 

 acting upon starch paste converts the starch into dextrin and maltose. 

 Saliva and pancreatic juice have a similar effect. Boiling with 

 dilute sulphuric acid converts it almost completely into dextrose. 



Dextrin is commonly prepared by heating potato starch by means 

 of superheated steam to 180 to 200 (yellow dextrin), or by mixing 

 the starch with 2 to 9 per cent, of nitric acid mixed with a little water 

 and heating in thin layers to HQ (white dextrin). Both varieties are 

 soluble in water. In yellow dextrin the form of the starch grain is 

 but little altered. 



Tapioca consists of the partially gelatinised starch from the 

 rhizomes of Manihot utilissima, Pohl (N.O. Euphorbiacece) ; the 



