DIASTASE CHANGES STARCH INTO SUGAR. il9 



examined, when the first true leaves of the plant have been fully 

 formed and expanded, the diastase will be found to have in great part, 

 if not entirely, disappeared. This substance, therefore, is first formed 

 when the seed begins to sprout, performs a functior which makes its 

 presence necessary at the base of the germ, and which function being 

 discharged when the true leaves are formed, it then disappears. What 

 is the nature of this temporary function, why the diastase must reside at 

 the base of the sprout in order to discharge it, and why it should so early 

 cease, will appear from a detail of the properties of this singular sub- 

 stance. 



Properties of diastase. — If the solution obtained from malt be digested 

 with potato, flour, or other starch, at a temperature between 120° and 

 140° F., the latter will gradually dissolve and will form a colourless 

 transparent solution. "When this solution is carefully evaporated a yel- 

 lowish white powder is obtained, perfectly soluble in water, to which 

 the name of dextrine has been given, [because its solution turns to the 

 right a ray of polarized light when passed through it.] This dextrine 

 has the same composition as starch. It is merely starch changed or 

 transformed in such a way as to become soluble in cold water, — a 

 change analogous to that which it undergoes by simply boiling in water. 

 ' But if the digestion be continued after the starch is dissolved, the so- 

 lution will gradually acquire a sweet taste, and if it be now evaporated 

 it will yield, instead of dextrine, a mixture of gum and grape sugar. 

 And if the digestion be still further prolonged, the whole of the starch 

 will be converted into grape sugar only. — [See above, § 6, p. 113.] 



Thus diastase (like sulphuric acid) possesses the property of trans- 

 forming starch entirely — first into gum, and then into grape sugar. The 

 intermediate stage of dextrine has not been recognized in the action of 

 sulphuric acid, nor is it easy to arre^r. the action of diastase exactly at 

 this point — the most carefully prepared dextrine always containing a 

 mixture of gum and sugar. One part of diastase will convert into sugar 

 2000 parts of starch. 



A solution of diastase, when allowed to stand, soon undergoes decom 

 position, and after being boiled, it has no further effect upon starch. It 

 has not been analysed, because it is diflScult to obtain it In a pure state. 

 It contains nitrogen, however, for, when moistened and exposed to the 

 air, it decomposes, and, among other products', yields ammonia.* 



The functions of diastase — one of the purposes at least for which it is 

 produced in the living seed, and situated at the base of the germ — will 

 now be in some measure understood. The starch in the seed is the food 

 of the future germ, prepared and ready to minister to its wants when- 

 ever heat and moisture concur in awakening it to life. But starch is it- 

 self insoluble in water, and could not, therefore, accompany the fluid sap 

 when it begins to move and circulate. For this reason diastase is 

 formed at the point where the germ first issues from the mass of food. 

 There it transforms the starch, and renders it soluble, so that the young 

 vessels can take it up and convey it to the point of growth. When the 

 starch is exhausted its functions cease. It is then itself transformed and 



• It will be recollected that ammonia contains nitrogen, bslng represented by NHs.—See 

 Lecture III., p, 51. 



