198 POWDERED VEGETABLE DRUGS 



10. (Figs. 11-32). AMYLUM, Starch. U. S. 

 Starke, G. Amidon, Fr. 



Corn starch is the official starch of the pharmacopoeia. There are 

 however other starches of commercial value and interest with which 

 the student should be familiar. The following more or less important 

 commercial starches are described: Rye, wheat, barley, corn, rice, 

 oat, bean, pea, lentil, potato, canna, banana, arrowroot (Queensland, 

 Indian, Siam), yam, and sago. Ash should not exceed 0.5 per cent. 



All starches are similar as to chemical composition, the formula 

 being C 6 Hio0 5 , or some multiple thereof. The specific gravity is 

 higher than that of water and the granules quickly settle out from water 

 suspensions and it is upon this property that the commercial production 

 of starch depends. The starch granule consists of granulose and 

 starch cellulose, the former constituting the greater bulk. The skele- 

 ton of cellulose may be obtained by digesting the granulose in saliva, 

 when it will be found that it is colored yellow with iodine. The amylo- 

 dextrine granules of mace, first described by Tschirch, consist largely 

 of amylodextrine which is isomeric with starch but which colors reddish- 

 brown with iodine, and contains only small amounts of granulose and 

 starch cellulose. 



Purified starches are similar as to certain gross characters, namely 

 snow white, odorless, tasteless (excepting the slightly sweetish taste 

 which is due the action of the ptyalin which converts some of the 

 starch into sugar) , and giving rise to a crisp crepitant feel when rubbed 

 or pressed between the fingers, in a cloth or paper container. Boiling 

 converts starch into a paste, and on boiling with dilute sulphuric or 

 hydrochloric acids it is successively changed into soluble starch, dex- 

 trine and dextrose. It is soluble in solutions of caustic soda or of 

 potash and for which reasons these substances are used for the purpose 

 of clearing up starch bearing sections of vegetable tissues. The 

 diastases convert starch into maltose and other closely related sacchar- 

 ine products. 



Although the starches are similar as to chemical composition, they 

 differ considerably as to physical properties (optical, morphological, 

 microscopical appearances) and in digestibility. Starches are not 

 digested at the same rate in the saliva, intestinal tract, or by the plant 

 diastases. Arrowroot starch (Mara*nta) is preferred for children and 

 invalids, because of its supposedly greater digestibility. It is perhaps 

 self-evident that the rate of digestion of starch also depends upon the 

 size of the granules. Dishes prepared from rice starch are more easily 

 or more quickly digested than are dishes made from potato starch or 

 from corn starch. 



