182 ALIMENTATION. 



when starch is taken uncooked. This change is generally effected, however, in the pro- 

 cess of cooking. 



The most interesting properties ot starch are connected with its transformation, first 

 into dextrine and finally into glucose. This always takes place in digestion, before starch 

 can be absorbed. In the digestive apparatus, the change into sugar is almost instan- 

 taneous, and the intermediate substance, dextrine, is not recognized. By boiling starch 

 for a number of hours with dilute sulphuric acid, it gradually loses its property of striking 

 a blue color with iodine, and is transformed, without any change in chemical composition, 

 into the soluble substance called dextrine. If the action be continued, it assumes four atoms 

 of water and is converted into glucose. If dextrine be perfectly pure, no coloration is 

 produced by the addition of iodine, but it ordinarily contains starch imperfectly trans- 

 formed, and iodine produces a reddish color. The change of starch into dextrine may be 

 effected by a dry heat of about 400 Fahr., a process which is commonly employed in 

 commerce. The most effectual method of producing this transformation of starch, aside 

 from the process of digestion, is by the action of a peculiar vegetable substance called 

 diastase. This substance is produced in the process of germination of many of the vege- 

 tables containing starch. 1 One part of diastase will effect the transformation of one hun- 

 dred parts of starch, which would require thirty times the quantity of sulphuric acid. 

 What has been said regarding sugar as an alimentary principle will apply to starch. 

 Although an abundant and important article of diet, it is insufficient of itself for the pur- 

 poses of nutrition. 



Vegetable Principles resembling Starch. In certain vegetables, substances isomeric 

 with starch, but presenting slight differences as regards general properties and reactions, 

 have been described, but they possess no very great interest as alimentary principles and 

 demand only a passing mention. These are, inuline, lichenine, cellulose, pectose, mannite, 

 mucilages, and gums. Inuline is found in certain roots. It is capable of being converted 

 into sugar but does not pass through the intermediate stage of dextrine. It differs from 

 starch in being very soluble in hot water and in striking a yellow instead of a blue color 

 with iodine. Lichenine is found in many kinds of edible mosses and lichens. It differs 

 from starch only in its solubility. 



Cellulose is a substance, generally regarded as identical in all plants, which forms the 

 basis of the walls of the vegetable cells. It exists in greater or less abundance in all 

 vegetables. It is less easily acted upon by acids than starch, but is capable, when treated 

 with concentrated sulphuric acid, of being converted first into dextrine, and finally into 

 sugar. It is only in soft and recent vegetable products that it can be regarded as an ali- 

 mentary principle. 



Pectose is a principle which exists, mingled with cellulose, in unripe fruits, carrots, 

 turnips, and some other vegetables of this class. Its composition has not been deter- 

 mined. In ripe fruits, it is found transformed into a soluble substance called pectine. 

 This transformation may be effected artificially by the action of acids and heat. Pectine 

 may be precipitated in a gelatinous form by alcohol from the juices of fruits. 



Mannite is a sweetish principle found in manna, mushrooms, celery, onions, and 

 asparagus. Manna in tears is composed of this principle in nearly a pure state. It is 

 perhaps more analogous to sugar than to starch, but it is not capable of fermentation and 

 has no influence on polarized light. 



Gums and mucilages may enter to a certain extent into the composition of food, but 

 they can hardly be considered as alimentary principles. Gums are found exuding from 

 certain trees, first in a fluid state, but becoming hard on exposure to the air. A viscid, 

 stringy mucilage is found surrounding many grains, such as the flax-seed and quince-seeds, 

 and exists in various kinds of roots and leaves. Both gums and mucilages mix readily 



1 Diastase is a white, amorphous, nitrogenized substance, insoluble in alcohol, soluble in water, and is extracted 

 from barley, oats, grain, and potatoes, in process of germination. Its action upon starch is most energetic at from 150* 

 to 167 Fahr. 



