1220 GALACTOSE. 



3. Galactose (Cerebrose). 6 H 12 O 6 . 



When milk sugar (lactose), see p. 1223, is boiled with dilute 

 mineral acids it is decomposed into a molecule of dextrose and 

 one of galactose — 



&■ 



^12^22^11 + H 2 = C 6 H 12 6 + C 6 H 12 6 . 



The two sugars may be separated by crystallization and by 

 taking advantage of the greater solubility of galactose in abso- 

 lute alcohol. In its general reactions and behaviour galactose 

 resembles dextrose but is possessed of a considerably greater 

 specific rotatory power [(a) D = +83°] which increases with the 

 concentration and rise of temperature. It yields with phenyl- 

 hydrazine an osazone (phenyl-galactosazone) which has the same 

 composition as phenyl-glucosazone and very similar solubilities. 

 It differs however from the latter in melting at 190 — 193° and 

 in being optically inactive when dissolved in glacial acetic acid. 

 It has recently been shewn that the sugar which results from 

 the action of boiling dilute sulphuric acid on certain constitu- 

 ents of the brain substance and has been named cerebrose, is 

 really identical with galactose. 



Galactose is fermentable with yeast, but less readily so than 

 is dextrose. 



4. Glycuronic acid. C 6 H 10 O 7 . [COH - (CH • OH) 4 - 

 COOH]. 



This acid was first obtained as a compound, campho-glycu- 

 ronic acid, in the urine of dogs after the administration of 

 camphor, and subsequently as urochloralic acid after the admin- 

 istration of chloral. Since then it has been found in urine as 

 ethereal or glucoside-like compounds with an extensive series 

 of members of the fatty or aromatic series after the introduc- 

 tion of the appropriate substances into the animal body. It is 

 probable that traces of compounds of this acid occur normally 

 in urine, since this excretion is usually slightly lsevorotatory 

 and it is known that indole and skatole which are formed in 

 the alimentary canal readily reappear in the urine as compounds 

 of glycuronic acid, viz. indoxyl- and skatoxyl-glycuronic acid, 

 when introduced into the body. The compounds of glycuronic 

 acid are all kevorotatory and some of them reduce metallic 

 salts on boiling and may hence lead to errors in the determina- 

 tion of sugar in urine. 



Glycuronic acid does not occur in the free state in the ani- 

 mal body. Chemically it is closely related to dextrose, and 

 like dextrose is dextrorotatory but to a less extent, reduces 

 Fehling's fluid to the same extent as does dextrose and forms 

 with phenyl-hydrazine a yellow crystalline compound which 



