NON-NITEOGENIZED ALIMENTARY PRINCIPLES. 59 



parent, and finally fuse together, mingling with the water, 

 and giving it a mucilaginous consistence. The mixture on 

 cooling forms a jelly-like mass of greater or less consistence. 

 This change in starch is called hyd ration, and is interesting 

 ' as one of the transformations which takes place in the pro- 

 cess of digestion, when starch is taken uncooked. This change 

 is generally effected, however, in the process of cooking. 



The most interesting properties of 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 instantaneous ; 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 ordinarily it contains 

 starch imperfectly transformed, and iodine produces a reddish 

 color. The change of starch into dextrine may be effected 

 by a dry heat of about 400 Fahr., a method which is com- 

 monly employed in commerce. 



The most effectual method of producing this transforma- 

 tion 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 vegetables containing starch. 1 Its exact chemical com- 

 position is unknown. One part of diastase will effect the 

 transformation of one hundred parts of starch, which would 

 require thirty times the quantity of sulphuric acid. 



1 Diastase is a white, amorphous, nitrogenized substance, insoluble in alcohol, 

 soluble in water, and is extracted from barley, oats, grain, and potatoes, in pro- 

 cess of germination. Its action upon starch is most energetic at from 150 to 

 167 Fahr. 



