CHEMICAL BASIS OF THE ANIMAL BODY. 1221 



melts at 114 — 115°. The acid is known only as a syrup soluble 

 in alcohol and water. It gives the reaction with phloroglucin 

 and yields furfuraldehyde as do the pentoses (see p. 1217). 



The formation of the compounds of glycuronic acid to which 

 attention has been drawn is of great and increasing interest. 



DlSACCHARIDES. 



The Cane-Sugar Grroup. 

 1. Saccharose (Cane-sugar). C 12 H 22 O n . 



Although it is not found as a constituent of any animal 

 tissue this sugar possesses no inconsiderable interest in view 

 of the fact that it is a food-stuff which is largely consumed 

 by man and may constitute in many cases no small part of the 

 total carbohydrates with which the body is supplied. 



Cane-sugar is chiefly distinguished from the others by the 

 fact that it does not reduce metallic salts, and does not form 

 a compound with phenyl-hydrazine, but the property which is 

 of greatest interest to the physiologist is the ease with which 

 it may be ' inverted ' or converted into equal parts of dextrose 

 and kevulose — 



C 12 H 22 O n 4-H 2 = C 6 H 12 6 (dextrose) + C 6 H 12 6 (hevulose). 



This inversion is readily brought about by treatment with dilute 

 mineral acids at 100° or even at 40° or below if the action is 

 more prolonged ; it is also the result of the action of enzymes, 

 more especially of invertin from yeast, and is characterized 

 experimentally by the change in the rotatory power of the 

 solution, which from being originally dextrorotatory becomes 

 lsevorotatory ; hence the name 'inversion.' For cane-sugar 

 («) D = +66° ; for hevulose («) D = —100°. The rotatory power 

 of the latter is largely dependent upon temperature and concen- 

 tration. 



When cane-sugar is injected into the blood-vessels or tissues 

 of an animal it is eliminated in an unaltered condition and is 

 thus shewn to be non-assimilable. On the other hand, it maj r be 

 introduced in large amounts into the alimentary canal without 

 reappearing externally in the urine. From this it may be con- 

 cluded that it undergoes some change before or during absorp- 

 tion and this change is most probably that of inversion. This 

 change may take place in the stomach, partly under the influ- 

 ence of the acid of the gastric juice but also as the result of the 

 action of a soluble enzyme ; it is even more marked in the small 

 intestine, where the active agent is without doubt an enzyme. 

 From this it appears that cane-sugar conforms to the apparently 

 general rule that the carbohydrates leave the alimentary canal 

 as dextrose. 



