FORMATION OF HIGHER CARBOHYDRATES 43 



hexoses and succeeded in isolating from it a small quantity 

 of a sugar acrose. Acrose can also be obtained by the 

 action of dilute caustic soda on glycerose, a substance obtained 

 by the oxidation of glycerol. From the acrose thus formed 

 Fischer was able by an elaborate series of reactions to prepare 

 ordinary fructose or levulose. In respect to the action of 

 weak alkalis, Spoehr found that sunlight had no action on a 3 

 per cent solution of formaldhyde in the presence of such salts 

 as calcium carbonate, potassium carbonate and potassium 

 nitrate in decinormal concentration, no trace of sugar being 

 found after an isolation period of four months. 



With regard to the formation of the higher carbohydrates 

 from fructose, practically nothing is known. Whilst the syn- 

 thesis of levulose from formaldehyde in vitro, and the con- 

 version of levulose into glucose are established facts, no 

 success has as yet attended attempts to synthesize sucrose 

 from its two hexose sugars, dextrose and levulose. In this 

 connexion, however, it may be mentioned that the synthesis 

 of disaccharides from monosaccharides has been achieved only 

 in a very few cases. Fisher 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 synthesized melibiose. Similarly iso- 

 maltose has been obtained by Croft-Hill f by the action of 

 maltase on glucose. 



It is obvious from this survey that the hypothesis of Baeyer 

 has influenced to a remarkable degree investigations on the 

 synthetic aspects of carbon assimilation ; this to a large extent 

 is psychological, for the hypothesis is attractive in that it is 

 plausible and lends itself readily to test tube investigation. 

 The evidence readily centres around distinct nuclei the identi- 

 fication in the plant of the critical initial intermediate products ; 

 the effect of presenting the plant with some of these initial sub- 

 stances in place of natural raw material ; and the elaboration 

 of the final from the supposed initial products in the laboratory 

 and may be briefly considered under these heads : 



Carbon Monoxide. This gas, if produced, must be fixed 



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

 t Croft-Hill: ' Journ. Chem. Soc.," Lond., 1898, 73, 634 ; see also Emmer- 

 ling : " Ber. deut. chem. Gesells," 1901, 34, 600, 2206. 



