354 AN AMERICAN TEXT-BOOK OE PHYSIOLOGY. 



the pancreas in some way for the normal consumption of 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 

 water in the tissues and in the liquids of the body is naturally absolutely 

 essential to the normal play of metabolism ; and conditions, such as muscular 

 exercise, that increase the water-loss bring about also an increased water- 

 consumption, the regulation being effected through the nervous mechanism 

 that mediates the sensation of thirst. The water taken into the body does 

 not, however, serve directly as a source of energy, since it is finally eliminated 

 in the form in which it is taken in ; it serves only to replace water lost from 

 the tissues and liquids of the body, and it furnishes also the menstruum for the 

 varied chemical reactions that take place. Continued deprivation of water 

 leads to intolerable thirst, the cause of which is usually referred to the altered 

 composition of the tissues gen era 11 y. including the peripheral nervous system. 



Inorganic Suits, — The essential value of the inorganic salts to the proper 

 nutrition of the body does not com moldy force itself upon our attention, since, 

 as a rule, we get our proper supply unconsciously with our food, without the 



sessity of making a deliberate selection. NaCl (common table-salt) forms 



an exception, however, to this rule. Speaking generally, inorganic salts do 

 not serve asa source of heat-energy to the body — that is, the reactions that 

 they may undergo are not accompanied by the transformation of a material 

 amount of chemical energy into heat. On the other hand, their presence and 

 distribution by virtue of their osmotic pressure may exercise an important 

 influence upon the movement of water in the body. Most of the salts found in 

 the urine and other excreta are eliminated in the same form in which thev 



