12 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



intermediate product in the formation of dextrose by mineral acids from 

 starch. An amylolytic ferment in blood serum, capable of forming 

 dextrose from starch, acts similarly. 1 A small quantity occurs in 

 normal urine. 2 It is readily soluble in water, is very sweet, and 

 ferments slowly with yeast. Its general characters are like those of 

 maltose, but its osazone forms fine yellow needles which melt at 150 C. 

 Lactose or milk-sugar occurs only in milk, and occasionally in the 

 first days of lactation in the urine in small quantities. 3 



It crystallises in rhombic prisms, which contain one molecule of water 

 of crystallisation (Fig. 3). It is soluble in six 

 parts of cold, and two and a half parts of hot 

 water; it is therefore less soluble than the 

 other sugar's. It has only a faint sweet 

 taste. Aqueous solutions are dextro-rotatory 

 / A * () D = + 59-3 (Hesse) 4 and +52-5 for the 



V 2 fy hydrate at 20 C. (Schmoger). 5 Its reducing 



_ power as tested by Fehling's solution is 



j) ~~J intermediate between that of dextrose and 



L - / maltose. 6 Lactose is very resistant to the 



FIG. 3. Lactose crystals. After inverting ferment of yeast, and so undergoes 

 lrey ' the alcoholic fermentation very slowly. It 



is, however, rapidly inverted by the Kephir fungus, and of all the 

 sugars is that most readily affected by the B. ladis; the lactic acid 

 fermentation occurs in two stages, as follow : 



>A<? 



1222n 2 36 , 



(lactose) (lactic acid) 



(lactic acid) (butyric acid) 



With phenylhydrazine, lactose yields phenyl-lactosazone, which readily 

 crystallises in needles (Fig 4). It is soluble in eighty to ninety parts 

 of boiling water. Its melting point is 200 0. 



Among the rarer disaccharides must be mentioned trelialose (from certain 

 fungi), and meleliose, a saccharose which with cMructose (levulose) is obtained 

 from raffinose. Raffinose 7 is an interesting sugar found in Eucalyptus manna, 

 cotton seeds, and barley. It is a trisaccharide, consisting of a combination 

 of dextrose, levulose, and galactose. 



The polysaccharid.es. To this group belong a large number of 

 carbohydrates of high molecular weight, and with the formula (C 6 H 10 5 ) n . 

 Their molecular weights differ a good deal, but have not yet been 

 determined directly by chemical methods. 8 They are not crystalline, 

 are indiffusible, and, as a rule, insoluble in cold water. In hot water 

 they partially dissolve, forming opalescent solutions. Like the proteids, 



1 Rohmann, CentralU. f. d. med. Wissenscli., Berlin, 1893, S. 849. 



2 Lemaire, Ztsclir. /. pliysiol. Chem., Strassburg, 1896, Bd. xxi. S. 442. 



3 The most recent observations on lactose in the urine of women after childbirth are by 

 Lemaire, Ztschr.f.physiol. Chem., Strassburg, 1896, Bd. xxi. S. 442. Pavy, Lancet, London, 

 1897, vol. i. p. 1075. See also Hofmeister, Ztschr.f. physiol. Chem. , Strassburg, Bd. i. S. 101. 



4 Ann. d. Chem., Leipzig, 1875, Bd. clxxvi. S. 98. 



5 Ber. d. deutsch. chem. Gesellsch., Berlin, 1880, Bd. xiii. S. 1922. 



6 Ten c.c. of Fehling's solution = '06334 lactose ; see footnote 1, p. 11. 



7 Loiseau, Compt. rend. Acad. d. sc., Paris, 1876, tome Ixxxii. p. 1058 ; Ber. d. deutsch. 

 chem. Gesellsch., Berlin, Bd. ix. S. 7-32; Scheibler, ibid., 1886, Bd. xix. S. 2868. 



8 By Raoult's method of determining the lowering of the freezing point in very dilute 

 solutions, Brown and Morris (Journ. Chem. Soc., London, 1888, p. 610), have provisionally 



