210 THE CARBOHYDRATES. 



Mannoses. d-Mannose, also called seminose, is obtained with d-levulose 

 on the careful oxidation of d-mannite. It is also obtained on the hydrolysis 

 of natural carbohydrates, such as salep slime and reserve cellulose (especially 

 from the shavings from the ivory-nut). It is dextrorotatory, readily ferments 

 with beer-yeast, gives a hydrazone not readily soluble in water, and an osazone 

 which is identical with that from d-glucose. 



Galactose (not to be mistaken for lactose or milk-sugar) is obtained 

 on the hydrolytic cleavage of milk-sugar and by hydrolysis of many other 

 carbohydrates, especially varieties of gums and mucilaginous bodies. 

 It is also obtained on heating cerebrin, a nitrogenized glucoside prepared 

 from the brain, with dilute mineral acids. 



It crystallizes in needles or leaves which melt at 168 G. It is some- 

 what less soluble in water than dextrose. It is dextrogyrate, and according 

 to NEUBERG 1 has a rotation (a) D =+81. With ordinary yeast galac- 

 tose is slowly, but nevertheless completely, fermented. It is fermented 

 by a great variety of yeasts (E. FISCHER and THIERFELDER) , but not by 

 Saccharomyces apiculatus, 2 which is of importance in physiologic al- 

 chemical investigations. Galactose reduces FEHLING'S solution to a 

 less extent than dextrose, and 10 cc. of this solution are reduced, accord- 

 ing to SOXHLET, by 0.0511 gram galactose in 1-per cent solution. Its 

 phenylosazone melts according to NEUBERG at 196-197 C., and is soluble 

 with difficulty in hot water, but with relative ease in hot alcohol. Its 

 solution in glacial acetic acid is optically inactive. In the test with 

 hydrochloric acid and phloroglucin galactose gives a color similar to that 

 of the pentoses, but the solution does not give the absorption spectrum. 

 On oxidation it first yields galactonic acid and then mucic acid, and 

 these serve in the detection of galactose. 



Levulose, also called ^-FRUCTOSE and FRUIT-SUGAR, occurs, as above 

 stated, mixed with dextrose extensively distributed in the vegetable 

 kingdom and also in honey. It is formed in the hydrolytic cleavage 

 of cane-sugar and several other carbohydrates, but it is very readily 

 obtained by the hydrolytic splitting of inulin. In extraordinary cases 

 of diabetes mellitus we find levulose in the urine. NEUBERG and STRAUSS 3 

 have detected levulose with positiveness in human blood-serum, and 

 exudates in certain cases. 



Levulose crystallizes with comparative difficulty in coarse crusts 

 or warts or in fine needles. G. MORNER 4 has obtained crystals 2-3 mm. 

 long which belonged to the rhombic system, and neither melted nor lost 

 in weight on heating to 100 C. The melting-point is 110 C. Levulose 



1 See C. Oppenheimer, Handb. d. Biocehm. 1, p. 197. 



2 See F. Voit, Zeitschr. f. Biol., 28 and 29. 



3 Zeitschr. f . physiol. Chem., 36, which also contains the older literature. 

 4 Svensk. Farmac. Tidskr, No. 6, 1907. See also Maly's Jahresb., 37, p. 95. 



