. Chemistry: general, medical, and pharmaceutical, including the chemistry of the U. S. Pharmacopia. A manual on the general principles of the science, and their applications in medicine and pharmacy. or diffused, white or colored, polarized or plain. Polarizedlight is especially valuable in developing differences and in intensi-fying the effects of obscure markings. By polarized light the gran-ules of potato starch appear as if traversed by a black cross ; wheatstarch-granules and many others also peculiarly and characteris-tically influence polarized light. Distinctive characters will some-t
. Chemistry: general, medical, and pharmaceutical, including the chemistry of the U. S. Pharmacopia. A manual on the general principles of the science, and their applications in medicine and pharmacy. or diffused, white or colored, polarized or plain. Polarizedlight is especially valuable in developing differences and in intensi-fying the effects of obscure markings. By polarized light the gran-ules of potato starch appear as if traversed by a black cross ; wheatstarch-granules and many others also peculiarly and characteris-tically influence polarized light. Distinctive characters will some-times present themselves only when the granules are made to rollover in the fluid in which they have been temporarily mounted orwhen the slide is gently warmed. Starches which have already beensubjected to the influence of heat—partly, as in sago or tapioca, oralmost entirely, as in bread—will of course differ in appearance from *By permission of Messrs. Longmans & Co. these engravings havebeen copied, with very few modifications, from the plates in two of thethree volumes of the original edition of Pereiras Materia Medica, STARCH. 475 STARCHES (Magnified 250 diameters). Figs. 42 to 476 ORGANIC CHEMISTRY. granules of the same starch before being dried, cooked, or characters of a starch will also somewhat vary according to theage and condition of the plant yielding it. The description of the microscopical characters of the officialvarieties of starch is as follows: 1. Wheat starch: A mixture oflarge and small granules, which are lenticular in form, and markedwith faint concentric striae surrounding a nearly central Maize starch: Granules more uniform in size, frequently polyg-onal, somewhat smaller than the large granules of wheat starch,and having a very distinct hilum, but without evident concentricstriae. 3. Rice starch : Granules extremely minute, nearly uniformin size, polygonal, hilum small and without striae. (For plates and descriptions of
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