286 VETERINARY PHYSIOLOGY 



The simplest carbohydrates are the monosaccharids, of 

 which glucose or dextrose or yrape sugar is the most 

 important. It is the sugar of the animal body. 



Closely allied to glucose in chemical composition is the 

 fructose or Icevidose, a sugar which, instead of rotating the 

 plane of polarised light to the right as glucose does, rotates 

 it to the left, but which in most other res])ects behaves like 

 dextrose. 



The other monosaccharid of importance is galactose, 

 a sugar produced by the splitting of milk sugar, and also 

 found in combination in the nerve tissue (p. 58). It does 

 not occur free in the body. 



These monosaccharids are easily tested for by boiling 

 their solution with Fehling's solution. A reddish precipitate 

 is formed. 



Under the influence of yeast they split into ethyl alcohol 

 and carbon dioxide, galactose, however, only very slightly. 



By the polymerisation of two monosaccharid molecules 

 with the loss of water, disaccharids, or double sugars, are 

 formed. Thus, two glucose molecules polymerise to form 

 one maltose molecule. 



0«Hi,Oe + CeH,„Oe = 2(C«H,,0e) - H,0 



= ^12^22^11 



Maltose is the sugar formed by the action of malt and 

 other vegetable and animal enzymes upon starch. By the 

 action of dilute acids and other agents it can be split into 

 two dextrose molecules. Like the monosaccharids it reduces 

 Fehliner's solution, and it ferments with veast. 



Lactose, the sugar of milk, is a disaccharid composed of a 

 molecule of dextrose united to a molecule of galactose with 

 dehydration. It readily splits into these two monosaccharids. 

 It reduces Fehling's solution, but it does not ferment with 

 yeast. 



Cane sugar or succose or saccharose consists of a mole- 

 cule of dextrose united to a molecule of lasvulose with the 

 elimination of a molecule of water. It does not reduce 

 Fehling. 



Monosaccharids anil disaccharids which are soluble 

 and crystalline substances are usually called sugars. 



