352 ESSENTIALS OF PHYSIOLOGY. 



and even when the animal is not receiving carbohydrate food. The 

 sugar in this case is not derived from carbohydrate, but is formed from 

 protein ; this is shown by the fact that in a starving animal the ratio 

 of the amount of dextrose in the urine to that of nitrogen, expressed 



as , becomes constant, varying in different animals from 2'5 to 3*5. 



Owing to the energy lost to the body as sugar, the tissues are compelled 

 to use an excessively large amount of protein as a source of energy, 

 and the rapid disintegration of protein increases the output of nitrogen 

 in the urine, the animal wastes, and its condition resembles that seen 

 in severe diabetes. 



(5) Experimental Diabetes. Von Mering and Minkowski were the 

 first to discover that the complete removal of the pancreas in dogs and 

 other animals is followed in a few hours by glycosuria, which soon 

 becomes very severe. The animals waste rapidly, the urine contains 

 /3-oxybutyric acid and acetone, as well as dextrose, and death occurs in 

 one to two weeks. .During life the urine contains an excess of sugar, 

 and after death the liver is found to be almost free from glycogen. 

 These symptoms are not due to the absence of the pancreatic juice 

 from the digestive tract, since ligature of the pancreatic duct does not 

 lead to glycosuria. Nor do they occur if a small portion, one-tenth or 

 more, of the pancreas is left in the body, although the subsequent 

 removal of this fragment is followed by the train of symptoms just 

 described. In diabetic animals the respiratory quotient is low, and 

 from this it has been inferred that the muscles and other tissues are 

 unable to make use of and to oxidise the sugar supplied to them in the 

 blood, with the result that hyperglycaemia occurs and sugar is excreted 

 by the kidneys. 



Further, it is generally assumed that the pancreas furnishes an 

 internal secretion, that is to say, some substance which passes directly 

 into the blood stream, and which links the sugar to the tissue cells ; 

 in the absence of this link the tissues are unable to take up sugar and 

 therefore cannot oxidise it. 



This view rests partly on the observation that w r hile neither muscle 

 juice alone nor a boiled extract of pancreas alone can destroy sugar 

 in vitro, muscle juice to which pancreatic juice is added does destroy 

 sugar. 



The formation of this internal secretion is attributed by many 

 observers to the islets of Langerhans, which are scattered throughout 

 the pancreas (fig. 130). The cells forming these islets differ in appear- 

 ance from the secretory cells of the acini of the pancreas, and contain 

 numerous fine granules which do not stain with eosin, as do the 



