70 PHYSIOLOGICAL CHEMISTRY 



ether. It gives all the reduction tests, ferments readily with 

 yeast, forms caramel on warming with alkali, and with phenyl- 

 hydrazine forms an osazone which melts at 205. It is perhaps 

 the most interesting of the sugars, for it is found in the blood, 

 and serves as one of the most valuable fuels for the body cells. 

 By the oxidation, or burning of glucose the cells produce heat 

 and do mechanical work. 



Fructose. (Levulose, Fruit Sug-ar.) Fructose is found in 

 plants chiefly combined with glucose as cane sugar, or in the 

 polysaccharide inulin from which it may be obtained by hydro- 

 lysis. It also occurs in honey. It is sometimes, though rarely, 

 found in the urine in a condition known as levulosuria. The solu- 

 bilities of fructose are similar to those of glucose. Its solution 

 rotates the plane of polarized light to the left, the specific rota- 

 tion being 92. It is called d-fructose because of its struc- 

 tural relationship to d-glucose, so that in this case the "d" does 

 not indicate that the compound is dextrorotatory. Solutions of 

 fructose show the phenomenon of mutarotation. Fructose is a 

 ketone sugar, and gives all the usual reduction tests for car- 

 bohydrates. It forms the same osazone as glucose, so that this 

 test is of no value to distinguish the two sugars. Fructose also 

 ferments with ordinary yeast. Fructose forms a calcium com- 

 pound which is much less soluble than that of glucose and serves 

 to separate the two sugars when they occur in a mixture. 



Fructose may be distinguished from glucose by its levorota- 

 tion, and also by the Seliwanoff reaction. On adding a few 

 crystals of resorcinol, and concentrated hydrochloric acid to a 

 levulose solution, and heating, a red color results. Glucose will 

 give the test under certain circumstances, however, so that it 

 must be carried out under definite conditions or it may lead to 

 erroneous conclusions. 



It also is possible to distinguish these sugars by means of 

 methylphenylhydrazine. With this substance, fructose and 

 other ketoses form osazones, whereas glucose and other aldoses 

 form only hydrazones. 



d-Galactose. Galactose occurs in nature as a constituent of 

 several gums, in the polysaccharide galactan in sea-weed, as a 



