60 CHEMICAL CONSTITUTION OF VEGETABLES. 



§ II.— PROXIMATE PRINMPLES WITH A TERNARY COM- 

 POSITION. 



OF STARCH. 



Starch is contained in the cells of vegetables under the form of 

 small white granuies which have no crystalline structure. 



In the year 1716, Leuwenhoeck ascertained that these granules 

 were globular bodies more or less regular in their contours. He 

 believed that he could perceive each globule enclosed in an envelope, 

 a kind of sac different in its nature from the matter which it con- 

 tained. M. Raspail, a few years ago, confirmed by his own re- 

 searches the observations of Leuwenhoeck ; he further attempted 

 to measure the diameter of the globules in different kinds of starch, 

 and came to the conclusion that their capsule is insoluble, and that 

 it is the internal part alone which is soluble in hot water.* Since 

 then MM. Payen and Pcrsoz have ascertained that if the globules 

 of starch be really surrounded l)y a capsule, it must be present in a 

 quantity scarcely appreciable — a quantity not exceeding ^A^^h of 

 the weight of the starch. These first researches were followed 

 by the subsequent observations of M. Payen, who has devoted him- 

 self to the study of the amylaceous prin<-iple with a zeal and perse- 

 verance which must secure him the gratitude of chemists and physi- 

 ologists. 



M. Payen has examined a vast number of foeculte microscopi- 

 cally ; the largest graiuiles he observed were ol)fained from one of 

 the varieties of potato, from the mcnispcnnum palmatiim, and the 

 canna gii^antea. 



The globules of starch frequently exhibit a polyhedral appearance, 

 a figure which evidently results fri)m their mutual pressure as they 

 iiave lain in the cells of the vegetable. Notwithstanding a great 

 general analogy of form, the granules of the starch of different 

 species of vegetables still present peculiar jthysiognomies, so that 

 they can be distinguished in many instances by the practised eye. 

 A character conuncui to the majority of fcDCula;, however, is round- 

 ness of contour, when their particles have not been compressed by 

 their contact in contiguous cells. 



Microscopical and chemical researches alike show that starch is 

 homogeneous in properties, as in composition ; that its globules are 

 composed of concentric layers, the external of which have exactly 

 the same characters as the internal layers. f In the natural state, 

 starch is insoluble in water and in alcohol ; it is very ductile, and 

 under the influence of certain agents it exhibits a great degree of 

 contractility. 



Feculas retain water with c«)nsiderable force ; the quantity rc- 



* In 1812, Vill.irs, in n paper on the structure of the potato, h;id nlrc.idy cstuvatcd 

 the volume of the slobulos of dirt'erent kinds of stJirrh. 

 t FrJtzche, Aunrles de Pogpondorf, t. xxxii. p. 1'20. 



