SYNTHESIS OF GRAPE SUGAR? 93 



etiolated plants, yields one or other of these acids, according to 

 the treatment to which it is subjected. 



(98.) The 5 -carbon compounds of artificial origin are of less 

 general interest. I may mention fousel oil or amyl-alcohol 

 C 5 Hi 2 O, and valerianic or valeric acid C 5 H 10 O 2 , a product 

 originally obtained from essential oil of valerian. By combining 

 amyl-alcohol with acetic acid we procure the pear flavour, and 

 by combining it with valeric acid, the apple or quince flavour 

 used in confectionery, which are probably identical with the 

 essential oils existing naturally in the ripe fruits. Again, by 

 combining valeric acid with glycerin we produce valerin, a 

 constituent of whale oil. 



(99.) Of the 6-carbon fatty compounds which have been 

 artificially obtained, the most interesting are caproic acid C6H 12 O 2 , 

 and leucic acid C6H 12 O 3 . Caproic acid is met with as a glyce- 

 ride in goat's butter, while amido-caproic acid or leu cine is an 

 occasional constituent of human urine, and a constant product of 

 the metamorphosis of glandular tissue. Starch C6H 10 O 5 , grape 

 sugar C6Hi 2 C>6, mannite C6Hi 4 06, and a host of allied alimentary 

 substances are also included in this group, though their exact 

 relationship to the typical members is not as yet clearly es- 

 tablished. Now, grape sugar has been obtained by Berthelot 

 from glycerin, which is itself, as I have said, obtainable by 

 purely inorganic means ; so that, in one sense, sugar may be 

 added to the list of artificially produced organic compounds. 

 Still the means employed for effecting the conversion of the 

 glycerin namely, the action of putrefying animal tissue must 

 prevent our regarding the resultant sugar as being strictly of 

 inorganic origin ; although formed exclusively out of the glyce- 

 rin, the animal tissue not having contributed any actual material 

 to its formation. However, if sugar has not yet been obtained 

 by a satisfactory process, the recent production of strictly allied 

 bodies, such as the propyl-phycite of Carius, together with our 

 increasing knowledge of the metamorphic relations of sugar itself, 

 assures us that an unexceptionable means for building up this 

 important alimentary principle cannot much longer escape us. 



