CARBOHYDRATES. 351 



Maltose, O 12 H 22 O U , is obtained by the action of diastase on starch. 

 Diastase is a substance formed during the germination of various 

 seeds (rye, wheat, barley, etc.), and it is for this reason that grain 

 used for alcoholic liquors is allowed to germinate, during which pro- 

 cess diastase is formed, which, acting upon the starch present, con- 

 verts it into maltose and dextrin: 



3(C 6 H 10 5 ) + H 2 : C 12 H 22 O n + C 6 H 10 5 . 

 Starch. Maltose. Dextrin. 



Maltose is also formed by the action of dilute sulphuric acid upon 

 starch, and is hence often present in commercial glucose; by further 

 treatment with sulphuric acid it is converted into dextrose. Maltose 

 crystallizes, reduces alkaline copper solutions, and ferments with 

 yeast. 



Melitose, C 12 H 22 O U , is the chief constituent of Australian manna. 



Milk-sugar, Saccharum lactis, C 12 H 22 O n + H 2 O === 36O (Lactose). 

 Found almost exclusively in the milk of the mammalia. Obtained 

 by freeing milk from casein aud fat and evaporating the remaining 

 liquid (whey) to a small bulk, when the milk-sugar crystallizes on 

 cooling. 



It forms white, hard, crystalline masses ; it is soluble in about 6 

 parts of water (at 15 C., 59 F.) and in 1 part of boiling water, 

 insoluble in alcohol and ether; it is much harder than cane-sugar, 

 and but faintly sweet ; it is not easily brought into alcoholic fermen- 

 tation by the action of yeast, but easily undergoes " lactic fermenta- 

 tion" when cheese is added. During this process milk-sugar i& 

 converted into lactic acid. 



Milk-sugar resembles grape-sugar in its action on alkaline solution 

 of copper, from which it precipitates cuprous oxide. 



Starch, Amylum, C 6 H 10 O 5 = 162. Starch is very widely dis- 

 tributed in the vegetable kingdom, and is found chiefly in the seeds 

 of cereals and leguminosse, but also in the roots, stems, and seeds of 

 nearly all plants. 



It is prepared from wheat, potatoes, rice, beans, sago, arrow-root, 

 etc., by a mechanical operation. The vegetable matter containing 

 the starch is comminuted by rasping or grinding, in order to open 

 the cells in which it is deposited, and then steeped in water; the 

 softened mass is then rubbed on a sieve under a current of water 

 which washes out the starch, while cellular fibrous matter remains on 



