306 LECTURE XIV. 



shown, however, that products of the vegetable kingdom which appar- 

 ently are not at all related to the carbohydrates, may, nevertheless, 

 have been derived from them. He showed that caoutchouc, a compound 

 containing an eight-carbon ring (1.5-dimethyl-cyclo-octadi-ine), on 

 hydrolysis yielded hevulinaldehyde, CH 3 . CO . CH 2 . CH 2 . COH, and 

 the ozonide of caoutchouc yielded similarly Isevulic acid. Now, the sugars 

 readily go over into Isevulic acid, while, on the other hand, it is also possible 

 that caoutchouc may be built up of pentoses. Their reduction to CsH 8 , 

 and subsequent condensation into 



CH 3 . G GH 2 GH 2 . GH \ 

 HC . CH 2 . CH 2 . C . CH 3 /X 



could account for the formation of caoutchouc. Perhaps the a-methyl- 

 furan, discovered by Atterberg l from beech-wood tar, which easily goes 

 over into Isevulinaldehyde, 2 may be even more closely related to the caout- 

 chouc synthesis. At all events, this gives us a new support for the assump- 

 tion that the whole large group of terpenes may likewise be derived from 

 the carbohydrates. 



In this connection we must not forget to mention a peculiar compound 

 which occurs in the vegetable kingdom, as well as in the animal organism, 

 and has the empirical formula of the hexoses. We refer to inositol (or 

 inosite). It is found in the muscles, liver, spleen, kidneys, suprarenal 

 bodies, lungs, brain, leucocytes, and the testes, and has often been noticed 

 in the urine under normal as well as pathological conditions. Inositol, 

 CeH^Oe, was formerly looked upon as a sugar. Maquenne 3 later recog- 

 nized it as a derivative of hexamethylene, with the following composition: 



OHOH CHOH 

 CHOH' ""CHOH 



x CHOH CHOH / 

 Hexahydroxybenzene = Inositol 



It is indeed possible that we have in this case, one of the first stages in 

 the conversion of a carbohydrate into the benzene ring, so that this 

 compound which is of so much biological interest opens up further possi- 

 bilities for the formation of the numerous aromatic compounds in the 

 plant organism. Although chemical investigation has often served to 

 give us better understanding concerning many obscure biological processes, 

 we must not forget that a clear conception is lacking in regard to the most 



1 A. Atterberg: ibid. 13, 879 (1880). 



8 C. Harries: ibid. 31, 37 (1898). 



8 Maquenne: Compt. rend. 104, 1719 (1887); ibid. 109, 812 (1889). 



