SUGARS 



47 



an enzyme maltase with the production of two molecules of 

 glucose. 



The sugars are readily distinguished from one another by 

 certain characteristic reactions. Thus glucose, fructose, and 

 maltose all reduce Fehling's solution (which contains cupric 

 oxide, Appendix II) with the formation of a red precipitate 

 of cuprous oxide, and are consequently known as reducing sugars. 

 Sucrose, on the other hand, is a non-reducing sugar, giving no 

 precipitate with Fehling's solution, until it has been inverted 

 by boiling or enzyme-action. It may be added that neither 

 inulin nor the dextrins effect reduction of this reagent. 



For microchemical purposes, especially when but small quan- 

 tities of sugars are present, the following procedure is more 

 advisable. The sections are mounted in a drop of a solution 



FIG. 22. Osazones. A, of glucose; B, of maltose (after Plimmer). 



of phenylhydrazine hydrochloride in glycerine with which a 

 drop of a solution of sodium acetate in glycerine (Appendix II) 

 is thoroughly mixed. The preparation is heated for about half 

 an hour (although a longer period is often necessary) and 

 allowed to cool. The phenylhydrazine reacts with many of the 

 sugars to form insoluble yellow crystalline compounds, known 

 as osazones. Glucose and fructose produce the same osazone, 

 whose crystals appear as long needles arranged in sheaves 

 (Fig. 22, A) ; that of maltose forms rosettes or plates of broad 

 needles (Fig. 22, B), whilst in the case of cane-sugar no osazone 

 is produced. 



Another method of storage of carbohydrate-material takes 

 the form of strongly thickened cell-walls (cf . p. 30 and Fig. 14, A), 

 as in many seeds (Date, Lupine, Coffee, etc.). Such walls consist 



