Chemical Constituents of the Animal Body. 195 



Reactions of Dextrose and Lcevulose. Both dextrose 

 and laevulose give rise on reduction to an alcohol, sorbitol, 

 of the formula 



CH.OH CH(OH) CH(OH)CH(OH)CH(OH) CH 2 -OH 

 In giving rise to an alcohol of such a formula they 

 behave as an aldehyde or ketone may be expected to do. 

 In other respects, also, dextrose and laevulose behave like 

 aldehydes and ketones. They reduce, for example, alkaline 

 solutions of cupric salts. The reagent generally employed 

 is known as Fehling's solution, which is generally prepared 

 in the following manner : 34'6 grammes of copper sulphate 

 (with water of crystallization) are dissolved in water, and 

 the solution is made up to 500 c.c. ; a second solution con- 

 taining 173 grammes of Rochelle salt (potassium sodium 

 tartrate) and 60 grammes of sodium hydroxide in 500 c.c. 

 is also prepared. Equal volumes of these two solutions are 

 mixed, and then warmed with the solution containing the 

 sugar. The reduction is indicated by the precipitation of 

 red cuprous oxide when the mixture is warmed. This 

 reaction can be employed for the quantitative estimation of 

 sugars in solutions, each individual sugar producing a 

 definite amount of precipitate when warmed with Fehling's 

 solution under certain standard conditions of experiment. 

 The amount of precipitate yielded by each sugar is deter- 

 mined under these standard conditions. The estimations can 

 be carried out either by gravimetric or volumetric methods, 

 of which a large variety have been suggested. The em- 

 ployment of Fehling's solution in one form or another is 

 the most usual one for the quantitative estimation of 

 sugars. In the volumetric methods the sugar solution is 

 added to the Fehling solution until the blue colour dis- 

 appears ; various indicators can also be employed. In the 

 gravimetric method, the weight of cuprous oxide produced 

 by a given amount of solution is determined. Under given 



