CHEMISTRY OF DIGESTION AND NUTRITION. 293 



H 2 O it is usually supposed to be preceded by a splitting of the sugar molecule. 

 The steps in the process are not definitely known ; according to one hypoth- 

 esis, the molecule first undergoes cleavage, with the formation of lactic acid 

 (C 6 H 12 O 6 = 2C 3 H 6 O 3 ), which is then oxidized. According to another hypoth- 

 esis, the sugar first breaks down, with the formation of alcohol and CO 2 , as in 

 the yeast fermentation outside the body. 



There have been discovered recently in connection with the pancreas a 

 number of facts that are interesting not only in themselves, but doubly so 

 because they promise, when more fully investigated, to throw some light on 

 the manner of consumption of sugar by the tissues. It has been shown by 

 Y. Mering and Minkowski l and others that if the pancreas of a dog is com- 

 pletely removed, the tissues lose the power of consuming sugar, so that it 

 accumulates in the blood and finally escapes in the urine, causing what 

 has been called " pancreatic diabetes." If a small part of the pancreas is 

 left in the body, even though it is not connected by its duct with the duo- 

 denum, diabetes does not occur. The inference usually made from- these 

 experiments is that the pancreas gives off something to the blood an internal 

 secretion which is necessary to the physiological consumption of sugar. 

 In what way the pancreas exerts this influence has yet to be discovered; 

 possibly it is through the action of a specific enzyme which helps to break 

 down the sugar ; possibly it is by some other means. But the necessity of 

 the pancreas in some way for the normal consumption o'f sugar by the tissues 

 generally seems to be indisputably established. It is a discovery of the utmost 

 importance in its relations to the normal nutrition of the body, and also 

 because of its possible bearing on the pathological condition known as diabetes 

 mellitus. In this latter disease the tissues, for some reason, are unable to 

 oxidize the sugar in normal amounts, and a good part of it, therefore, escapes 

 through the urine. The facts and theories bearing upon diabetes are of 

 unusual interest in connection with the nutritive history of the carbohydrates, 

 but for a fuller description reference must be made to more elaborate works. 



Another statement in connection with the fate of sugar in the body is 

 worthy of a brief reference : It has been asserted by Lepine and Barral that 

 there is normally present in blood an enzyme capable of destroying sugar. 

 Their theory rests upon the undoubted fact that sugar added to blood outside 

 the body soon disappears. They call the process " glycolysis," and the enzyme 

 to which they attribute this disappearance the " glycolytic enzyme." Others, 

 however (Arthus), have claimed that this enzyme is only a post-mortem result 

 of the disintegration of the corpuscles of the blood, and that it is not present 

 in circulating blood. We must await further investigation upon this point, 

 and be content here with a mere reference to the subject. 



Nutritive Value of Water and Salts. Water is lost daily from the body 



in large quantities through the kidney, the skin, the lungs, and the feces, and 



it is replaced by water taken in the food or separately, and partially also by 



the water formed in the oxidations of the body. A certain percentage of 



1 Archiv fur experimentelle Pathologic u. Pharmakologie, 1893, xxxi. p. 85. 



