354 VETERINARY PHYSIOLOGY 



15 per cent. In fasting the only possible sources of this 

 sugar are the proteins and the fats of the body, (a) That 

 proteins are a source of sugar is shown by the fact that, in 

 diabetic patients and in dogs rendered diabetic by removal 

 of the pancreas, i.e. in animals which are excreting and not 

 using the sugar (p. 857), the output of sugar is increased by 

 giving proteins. It has further been found that most of the 

 amino-acids which build up the proteins, undergo the same 

 change, the non-nitrogenous part being to a greater or less 

 extent converted to sugar, the nitrogenous part being excreted 

 as urea. Claude Bernard had discovered that, after feeding 

 a dog, which had fasted till all the stored carbohydrates of 

 the liver had disappeared, on lean beef, glycogen, the 

 precursor of sugar, appeared in the liver. 



Qj) The question of whether the liver can form sugar 

 from the fats of the body is more difficult to answer. The 

 argument in favour of such a conversion is that in many 

 cases of pancreatic diabetes the amount of sugar formed is 

 more than could be derived from the proteins decomposed, 

 as indicated by the nitrogen excreted. Hence, it would 

 seem that it must be derived from the fats. 



(2) Storing Sugar as Glycogen. — The liver not only 

 manufactures sugar for the muscles when the supply from 

 outside is cut off, but it also has the power of storing sugar 

 derived from an excess of carbohydrates in the food, or from 

 an excess of proteins. This it does by converting the 

 monosaccharid into a polysaccharid — animal starch, or 

 glycogen. This substance accumulates in the protoplasm of 

 the cells, and its presence may be demonstrated by staining 

 with iodine. Since the same glycogen is derived from all 

 the single sugars, leevulose (a ketose) as well as dextrose (an 

 aldose), the liver protoplasm must perform a chemical change 

 in the process of synthesising them into glycogen, from 

 which dextrose alone is formed. The storasfe of oflvcosfen 

 may be very great, amounting in certain conditions to as 

 much as 10 per cent, of the weight of the liver. 



(3) Conversion of Glycogen to Dextrose. — When sugar is 

 required by the muscles, it is again converted to glucose, 

 and passes off in the blood. This subsequent conversion of 



