i64 THE CARBOHYDRATES 



and all attempts to synthesize cane sugar from glucose and 

 fructose, or from invert sugar, have hitherto failed. Fischer 

 and Armstrong* were able to synthesize a disaccharide — 

 isolactose — by the action of an enzyme, Kefir lactase, on a 

 mixture of glucose and galactose ; the same authors also syn- 

 thesized melibiose. Similarly isomaltose has been obtained by 

 Croft-Hill t by the action of maltase on glucose. 



The cane sugar is often supposed to be assimilated by the 

 protoplasm, which in turn forms the starch ; finally the maltose 

 may be formed from the starch, or by the condensation of 

 dextrose which has already been accomplished in the labora- 

 tory. 



In conclusion, mention should be made of a photosynthesis 

 of carbohydrate in the absence of chlorophyll which was 

 effected by Stoklasa and Zdobnicky.t Light from a quartz 

 mercury lamp was allowed to pass through a mica window 

 into a vessel containing a mixture of carbon dioxide and 

 hydrogen ; formaldehyde was slowly produced and this, in 

 presence of caustic potash, was polymerized with formation of 

 a sugar or mixture of sugars which was optically inactive and 

 not fermentable by yeast. The authors suggest that the 

 chlorophyll in plants acts as a means of absorbing ultra-violet 

 rays. 



According to Lob,§ however, these conclusions are not 

 justified by the experiments performed by Stoklasa and 

 Zdobnicky. 



With regard to the reverse process, Bertholet and Gau- 

 dechon II found that carbohydrates are decomposed by sunlight 

 and by ultra-violet light from a mercury lamp. The pro- 

 ducts of decomposition are carbon monoxide, carbon dioxide, 

 methane and hydrogen ; aldehydic sugars differ from ketonic 

 sugars both in the readiness with which they are decomposed 

 and in the composition of the gaseous mixtures produced. 



* Fischer and Armstrong: " Ber. deut. chem. Gesells.," 1902, 35, 3144. 



t Croft-Hill: "J. Chem. Soc, Lond.," 1898, 73, 634; see also Emmerling : 

 '♦ Ber. deut. chem. Gesells.," 1901, 34, 600, 2206. 



X Stoklasa and Zdobnicky: "Chem. Zeit.," 1910, 945. 



§Lob: "Biochem. Zeitschr.," 1912, 43, 434. 



II Bertholet and Gaudechon : " Compt. rend.," igio, 151, 395; 1912, 155, 

 401, 831. 



