CRUDE DRUGS. 643 



Corn Starch. — In fine powder or irregular, angular, white, 

 inodorous, tasteless masses ; grains somewhat spherical, but usually 

 polygonal, with a lenticular, circular or triangular point of origin 

 of growth, about 10 to 25 fi in diameter (Fig. 316, D). Corn starch 

 grains differ in structure in the different varieties (p. 229). 



Wheat Starch. — Usually in a fine powder consisting of 

 nearly spherical or ellipsoidal grains with point of origin of 

 growth and lamellae more or less indistinct, about 15 to 40 ju, in 

 diameter (Fig. 316, C). 



Rice Starch. — Usually in a grayish-white powder consisting 

 of minute angular grains about 5 to 8 /* in diameter and with 

 point of origin of growth and lamellae indistinct. 



Starch is insoluble in cold water or alcohol, but forms a white 

 jelly when boiled with water, which, when cool, gives a deep-blue 

 color with iodine and should give a neutral reaction to litmus 

 paper (commercial cornstarch is usually alkaline) ; ash not more 

 than I per cent. 



Structure of Starch Grains. — See Figs. 95, 96, 97, 316, .317. 



CoMPOSiTroN of Starch Grains. — See p. 162. 



ACACIA.— GUM ARABIC— A dried, gummy exudation 

 from the stem and branches of Acacia Senegal and probably other 

 species of Acacia (Fam. Leguminosse), trees (Fig. 153) growing 

 in sandy soil and forming forests in tropical Africa (p. 294). 

 The gum exudes spontaneously from the bark of the tree and is 

 apparently formed by the action of a ferment on the cell-contents 

 as it does not contain any remains of cell walls. The trees are 

 also incised, which increases the production of gum. The more 

 or less hardened pieces are collected and then sorted into different 

 grades, the market supplies being obtained from Egypt by way 

 of Alexandria (Kordofan gum), from the Soudan by way of 

 Suakin (" Tufkey sorts " and " Trieste picked "), and from Sene- 

 gambia by way of the port of St. Louis. The Kordofan gum is 

 considered to be the best. 



Description. — In roundish tears of variable size, or broken 

 into angular fragments ; externally whitish or yellowish-white, 

 with numerous minute fissures; translucent; very brittle, with a 

 glass-like, sometimes iridescent fracture; nearly inodorous; taste 

 mucilaginous. 



