58 ALIMENTATION. 



Starch may be separated from many plants by simple 

 washing, but in others in which it exists in connection with 

 a considerable proportion of gluten, a more elaborate pro- 

 cess is employed in commerce. The different varieties of 

 manufactured starch, such as corn-starch, potato-starch, 

 arrow-root, tapioca, and sago, differ only in the presence 

 of a minute quantity of odorous and flavoring principles. 



"When extracted in a pure state, starch is in the form of 

 granules, varying in size from y^foo- to ^^ of an inch, and 

 presenting, in most varieties, certain peculiarities of form. 

 The granule is frequently marked by a little conical excava- 

 tion called the hilus, and the starch substance is arranged in 

 the form of a concentric laminae, the outlines of which are 

 frequently quite distinct. When starch is rubbed between 

 the fingers, these little hard bodies give it rather a gritty 

 feel, and produce a crackling sound. Most chemists are of 

 the opinion that the starch-granules are composed of a single 

 substance, but some contend that each grain is a true vege- 

 table organ, with an investing membrane composed of nitro- 

 genized matter. 1 The different varieties of starch may be 

 recognized microscopically by the peculiar appearance of the 

 granules. 



The presence of even a minute quantity of starch in any 

 mixture which is not alkaline may be readily determined by 

 the addition of iodine, which unites with the starch, pro- 

 ducing an intense blue color. The color may be destroyed 

 by the addition of an alkali, or by the application of heat. 

 It may be restored, however, by the addition of an acid, or, 

 in the latter instance, it returns when the mixture is al- 

 lowed to cool, if the temperature has not been carried to 

 212 Fahr. 



Starch is insoluble in water ; but when boiled with several 

 times its volume of water, the granules swell up, become trans- 



1 BLONDLOT, Recherclies sur la Digestion des Matieres Amylacees, Nancy, 1853, 

 p. 13. 



