CARBOHYDRATES. 383 



constitution is concerned, they may be regarded as fatty bodies, as hexatomic alcohols, in 

 which 2H are wanting. 

 They are divided into the following groups : 



1. Division. Glucoses (C 6 H 12 6 ). (1) Grape-sugar (glucose, dextrose, or diabetic sugar) 

 occurs in minute quantities in the blood, chyle, muscle, liver (?), urine, and in large amount in 

 the urine in diabetes mellitus ( 175). It is formed by the action of diastatic ferments upon 

 other carbohydrates, during digestion. In the vegetable kingdom, it is extensively distributed 

 in the sweet juices of many fruits and flowers (and thus it gets into honey). It is formed from 

 cane-sugar, maltose, dextrin, glycogen, and starch, by boiling with dilute acids. It crystallises 

 in warty masses with one molecule of water of crystallisation ; unites with bases, salts, acids, 

 and alcohols, but is easily decomposed by bases ; it reduces many metallic oxides ( 149). 

 Fresh solutions have a rotatory power of +106. By fermentation with yeast it splits up into 

 alcohol and C0. 2 ( 150) ; with decomposing proteids it splits into 2 molecules of lactic acid 

 ( 184, I.); the lactic acid splits up under the same conditions in alkaline solutions, into 

 butyric acid, C0 2 , and H. For the qualitative and quantitative estimation of glucose, see 149 

 and 150. In alcoholic solution, it forms very insoluble compounds with chalk, barium, and 

 potassium, and it also forms a crystalline compound with common salt (Estimation, 150). 



(2) Galactose, obtained by boiling milk-sugar (lactose) with dilute mineral acids ; it 

 crystallises readily, is very fermentable, and gives all the reactions of glucose. When oxidised 

 with nitric acid it becomes transformed into mucic acid. Its specific rotatory power = +88 "08. 



(3) Laevulose (left-fruit-, invert-, or mucin-sugar) occurs as a colourless syrup in the acid 

 juices of some fruits and in honey ; is non-crystallisable, and insoluble in alcohol ; specific 

 rotatory power = - 106. It is formed normally in the intestine ( 183), and occurs rarely as a 

 pathological product in urine. 



II. Division. This contains carbohydrates with the formula C 12 H 22 O n , and its members 

 may be regarded as anhydrides of the first division 1. Milk-sugar or lactose occurs only in 

 milk, crystallises in cakes (with 1 molecule of water) from the syrupy concentrated whey ; it 

 rotates polarised light to the right = +59*3, and is much less soluble in water and alcohol than 

 grape-sugar. When boiled with dilute mineral acids it passes into galactose, and can be 

 directly transformed into lactic acid only by fermentation ; the galactose, however, is capable of 

 undergoing the alcoholic fermentation with yeast (Koumiss preparation, 232). For its 

 quantitative estimation ( 231). Rare in urine ( 267). 



2. Maltose (C 12 H 22 O n ) + H 2 (O y Sullivan) has 1 molecule of water less than grape-sugar 

 (C 12 H 24 12 ), is formed during the action of a diastatic ferment, such as saliva upon starch 

 ( 148) ; is soluble in alcohol, right-rotatory power = +150; it is crystalline, while its reducing 

 power is only two-thirds that of dextrose. [The ratio of the reducing power of maltose to that 

 of glucose is 100 to 66.] 



(3. Saccharose (cane-sugar) occurs in sugar-cane and some plants, it does not reduce a 

 solution of copper, is insoluble in alcohol, is right-rotatory, and not capable of fermentation. 

 When boiled with dilute acids, it becomes changed into a mixture of easily fermentable glucose 

 (right-rotatory) and laevulose (invert sugar, 183, 5, and 184, I., 6), Avhich ferments with 

 difficulty and is left-rotatory ( 183). When oxidised with nitric acid, it passes into glucic acid 

 and oxalic acid. ) 



(4. Melitose, from Eucalyptus-manna ; Meleztose, from Larch-manna ; Trehalose (My cose), 

 from Ergot : are all right-rotatory, and do not reduce alkaline cupric solutions). 



III. Division. This contains carbohydrates, with the formula, C 6 H 10 O 5 , which may be 

 regarded as anhydrides of the second division. 



1. Glycogen, with a dextro-rotatory power of 211, does not reduce cupric oxide. It occurs 

 in the liver ( 174), muscles, many embryonic tissues, the embryonic area of the chick (Kiilz), 

 in normal and pathological epithelium ; in diabetic persons it is widely distributed ; brain, 

 pancreas, and cartilage ; and in the spleen, pancreas, kidney, ovum, brain, and blood, together 

 with a small amount of glucose (Pavy). It also occurs in the oyster and some of the molluscs 

 (Bizio), and indeed in all tissues and classes of the animal kingdom. 



2. Dextrin was discovered by Limpricht in the muscles of the horse. It is right-rotatory = 

 + 138, soluble in water, and forms a very sticky solution, from which it is precipitated by 

 alcohol or acetic acid ; it is tinged slightly red with iodine. It is formed in roasted starch, 

 (hence it occurs in large quantity in the crust of bread see Bread, 234), by dilute acids, and 

 in the body by the action of ferments ( 148). It is formed from cellulose by the action of 

 dilute sulphuric acid. It occurs in beer, and is found in the juices of most plants. 



3. Amylum or Starch occurs in the "mealy" parts of many plants, is formed within 

 vegetable cells, and consists of concentric layers with an excentric nucleus (fig. 239). The 

 diameter and characters of starch-grains vary greatly with the plant from which they aie 

 derived. At 72 C. it swells up in water and forms a mucilage ; in the cold, iodine colours it 

 blue. Starch-grains always contain more or less cellulose and a substance, erythrogranulose, 

 which is coloured red with iodine ( 148) It and glycogen are transformed into dextrose by 

 certain digestive ferments in the saliva, pancreatic, and intestinal juices, and artificially by 

 boiling with dilute sulphuric acid. 



