THE CARBOHYDRATES. 465 



the right or to the left. Heated dry they give off the odor of caramel. They stain 

 red with thymol and sulphuric acid. According to their constitution, they may be 

 considered as fatty bodies, as hexatomic alcohol in which 2 atoms of H are wanting. 

 In small amounts the carbohydrates are constituents of almost all animal tissues. 

 In the presence of special nutritive disturbances decomposition of complex organic 

 constituents of the viscera appears to take place. Nitrogenous products that are 

 readily decomposed into urea are split off from the albuminates, and in addition 

 to these the non-nitrogenous portion appears as carbohydrate. The formation of 

 carbohydrates (sugar) from fats occurs in the germination of seeds containing oil, 

 with the taking up of oxygen. 



The carbohydrates can be divided into the following groups : 



1. The monosaccharids or glucoses, which contain only one molecule of simple 

 sugar: C 6 H 12 O 6 . i. Grape-sugar (glucose, dextrose, lump-sugar, starch-sugar, liver- 

 sugar or urinary sugar) has been produced synthetically by E. Fischer. It occurs 

 in the animal body in small amounts in the blood, chyle, muscle, liver, urine; 

 in large amounts in the urine in cases of diabetes mellitus. It is formed in the 

 process of digestion by diastatic ferments from other carbohydrates. In the 

 vegetable kingdom it is distributed in the sweet juices of many fruits and flowers, 

 and thence into honey. It is formed from cane-sugar, maltose, dextrin, glycogen 

 and starch on boiling with dilute acids. It crystallizes in cauliflower-like, warty 

 masses, with one molecule of water of crystallization, combines with bases, salts, 

 acids and alcohols, but is readily decomposed by bases. It exerts a reducing 

 action on many metallic oxids. Phenylglucosazone melts at a temperature of 

 204 C. As a result of its oxidation there develop first the monobasic glyconic 

 acid and then the monobasic glucic acid. A fresh solution has a rotatory power 

 of +106, which falls to +56. On fermentation with yeast it is decomposed 

 into alcohol and carbon dioxid; by putrefactive bacteria it is broken up into 

 two molecules of lactic acid. The qualitative and quantitative estimation of 

 grape-sugar is discussed on pp. 267, 268, and 501. In alcoholic solution it enters 

 into almost insoluble combinations with calcium, barium or potassium; also 

 with sodium chlorid it crystallizes into a combination. 



2. Galactose is formed by hydrolytic decomposition of milk-sugar (lactose), 

 but also by hydrolysis of gum and mucoid substances; and as a decomposition- 

 product of the glucosid, cerebrin. It forms needles and plates, soluble in water, 

 is dextrorotatory + 88.08 and fermentable and yields the reactions of dextrose. 

 Its phenylosazone melts at 193 C. When oxidized it forms galactonic acid and 

 later mucic acid. 



3. Levulose (levorotatory fruit-sugar, invert-sugar or mucous sugar) is formed 

 from inulin by the action of acids together with levulin, which is the analogue of dex- 

 trin. It occurs in the acid juices of some fruits and in honey as a colorless syrup, crys- 

 tallizable with difficulty, fermentable with greater difficulty, insoluble in cold 

 alcohol, with a rotatory power of 106. It reduces like dextrose and has the 

 same osazone. It is formed normally in the intestine and is rarely found abnor- 

 mally in the urine. 



II. Disaccharids or saccharoses contain two molecules of simple sugar, and hav- 

 ing the formula C 12 H 22 O U , are the anhydrids of the members of the first division. 



1. Milk-sugar (lactose = dextrose + galactose) occurs only in milk, crystal- 

 lizes in crusts, with i molecule of water, from whey evaporated to a syrupy con- 

 sistence, is dextrorotatory +52.5, soluble with greater difficulty than grape-sugar 

 in water and particularly in alcohol. On boiling with dilute mineral acids it is 

 decomposed into galactose and dextrose; it can be transformed directly into 

 lactic acid only by fermentation, and the resulting galactose is, however, sus- 

 ceptible of alcoholic fermentation with yeast (preparation of koumiss). Its quan- 

 titative estimation is discussed on p. 422. It occurs rarely in the urine. Lacto- 

 sazoiie melts at 200 C. 



2. Maltose (malt-sugar), C 12 H 22 O 12 + H 2 O, contains one molecule of water less 

 than two molecules of grape-sugar (C 12 H 24 O 12 ) and results in the diastatic decomposi- 

 tion of starch. It is soluble in alcohol", but is precipitated from an alcoholic solution 

 by ether in the form of needles (dextrose is not). It is dextrorotatory 138.4 and 

 crystallizable, and 100 parts reduce equally with 66 of dextrose. Dextrose reduces 

 cupric acetate, while maltose does not. Maltosazone melts at 208 C. Isomaltose 

 is not susceptible of fermentation. 



3. Saccharose (cane-sugar or beet-sugar = dextrose + fruit-sugar) is present 

 in cane-sugar and a number of plants, but it does not reduce copper. It is soluble 

 in alcohol with difficulty, is dextrorotatory and not fermentable. In the intestine, 

 and also when boiled with dilute acids, it is transformed into a mixture of glucose 



30 



