THE CARBOHYDRATES 65 



Maltose is produced as the result of hydrolytic changes either by 

 the action of acids or of enzymes upon starch. It is readily soluble 

 in water, and fairly soluble in alcohol. Its solutions are dextro- 

 rotatory: [a] D = 137-139. It ferments readily with yeast. It gives 

 the same reduction tests as dextrose, with the exception of Barfoed's. 

 The osazone is difficult to prepare, requiring warming for as long as 

 one and a half hours. The crystals are characteristic in shape, 

 being coarser than those of dextrososazone. Their melting-point 

 is 205. 



Lactose is the characteristic animal sugar, being found only in 

 milk, and occasionally in the urine of pregnant women. It dissolves 

 fairly readily in water, has a faint sweetish taste, and is insoluble 

 in alcohol. Its solutions are dextrorotatory, and [a] D = 52-5. With 

 the exception of Barfoed's it gives all the reduction tests. Its 

 osazone forms characteristic rosettes, and has a melting-point 

 of 201 C. With nitric acid it yields mucic acid crystals. It is not 

 iermentable with pure yeast, but it undergoes alcoholic fermentation 

 with the " kephir " fungus. With this fungus an alcoholic drink is 

 prepared chiefly from mare's and camel's milk. 



SECTION III. 



The Polysaccharides. This group includes the more complex 

 carbohydrates, such as the dextrins and vegetable gums, starches and 

 celluloses. They are characterized by the large size of their molecule, 

 being therefore colloidal in nature. 



The Celluloses (C 6 H 10 O 3 )n. Plant cellulose is in reality a mixture 

 of celluloses. These bodies are insoluble in hot or cold water, 

 alcohol, ether, and dilute acids or alkalies. They are soluble, 

 however, in ammoniacal copper oxide solution (Schweitzer's re- 

 agent), from which they are precipitated by acids. When acted 

 upon with strong sulphuric acid, cellulose yields a substance known 

 as amyloid, which gives a blue colour with iodine solution; by pro- 

 longed treatment dextrose is produced. By the action of strong 

 nitric acid, explosives (nitro-celluloses) such as gun-cotton are 

 produced. 



In the intestinal tract, particularly of herbivora, the enzyme known 

 as cytase partially decomposes cellulose. 



The Starches (C 6 H 10 5 )ra are a reserve food of wide distri 

 bution in the vegetable kingdom, being stored as grains shaped in 

 various forms in seeds (the cereals), tubers (potatoes), etc. As a 

 commercial product starch is a white amorphous powder without taste 

 or smell, insoluble in cold water, but yielding an emulsion with 

 hot water. A starch emulsion is best made by mixing starch to a 

 paste in the cold, and gradually stirring this into boiling water, a well- 

 known domestic process. By the action of the boiling water the starch 

 grains are made to swell up and break, and the starch is converted 



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