THE CHEMICAL COMPOSITION OF THE BODY. [CH. xxv. 



of these groups, and the most important members of each, are as 

 follows : 



The -f- and signs in the above list indicate that the sub- 

 stances to which they are prefixed are dextro- and levo-rotatory 

 respectively as regards polarised light. (See Polarimeter, p. 402.) 



The formulae given above are merely empirical ; and there is 

 no doubt that the quantity n in the starch group is variable and 

 often large ; hence the name poly sacchar ides that is given to 

 the group. Research has, moreover, shown that the glucoses 

 are either aldehydes or ketones of hexatomic alcohols C 6 H 8 (OH) 6 . 

 Thus dextrose is the aldehyde of sorbite, levulose the ketoue of 

 mannite, and galactose the aldehyde of dulcite. The amyloses may 

 be regarded as the anhydrides of the glucoses [uC 6 H 12 6 nH 2 = 

 (C 6 H 10 5 ) n ]. The sucroses are condensed glucoses i.e. they are 

 formed by the combination of two molecules of glucose with 

 the loss of one molecule of water (C 6 H 12 6 -|-C6H 12 6 H 2 = 

 Ci 2 H 22 11 ) ; hence the term disaccharide. The following are the 

 chief facts in relation to each of the principal carbohydrates : 



Dextrose or Grape Sugar. This carbohydrate is found in 

 fruits, honey, and in minute quantities in the blood and numerous 

 tissues, organs, and fluids of the body. It is the form of sugar 

 found in large quantities in the blood and urine in the disease 

 known as diabetes. 



Dextrose is soluble in hot and cold water and in alcohol. It is 

 crystalline, but not so sweet as cane sugar. When heated with 

 strong potash certain complex acids are formed which have a 

 yellow or brown colour. This constitutes Moore's test for sugar. 

 In alkaline solutions dextrose reduces salts of silver, bismuth, 

 mercury, and copper. The reduction of cupric to cuprous salts 

 constitutes Trammer's test, which is performed as follows : put a 

 few drops of copper sulphate into a test-tube, then solution of 

 dextrose, and then strong caustic potash. On adding the potash a 

 precipitate is first formed which dissolves forming a blue solution. 

 On boiling this a yellow or red precipitate (cuprous hydrate or 

 oxide) forms. 



