MINERAL MATTERS, WATER, ETC. 445 



intracellular ferment in the glycogenic cells. Such an enzyme has been iso- 

 lated for the liver. It is this enzyme that converts the liver glycogen to dex- 

 trose after death, and which is destroyed by boiling in the usual process of 

 isolating glycogen from the liver or other tissues. 



Glycosuria. Sugar may be present to excess not only in the hepatic 

 veins, but in the systemic blood. When such is the case, the sugar is ex- 

 creted by the kidneys, and appears in variable quantities in the urine. This 

 condition is known as glycosuria. 



Glycosuria may be experimentally produced by puncture of the medulla 

 oblongata in the region of the vaso-motor center, puncture diabetes. The 

 better fed the animal, the larger is the amount of sugar found in the urine 

 following this operation. In the case of a starving animal no sugar appears. 

 It is, therefore, highly probable that in puncture diabetes the sugar comes 

 from the hepatic glycogen, since in the one case glycogen is in excess, and in 

 the other it is almost absent. The nature of the change of nervous influence 

 is uncertain. This influence may be exercised in dilating the hepatic vessels, 

 or possibly may be exerted on the liver cells themselves. 



Many other circumstances will cause glycosuria. It has been observed 

 after the administration of various drugs, e.g., strychnine; phloridzin, a glu- 

 coside, and its derivative phloretin, which is not a glucoside; morphine; 

 adrenalin; nitrite of amyl, etc.; after the injection of curari, poisoning with 

 carbon dioxide gas, the inhalation of ether, chloroform, etc., the injection of 

 oxygenated blood into the portal venous system. Glycosuria has been 

 observed in man after injuries to the head and in the course of various 

 diseases. In such cases the glycosuria appears to be due either to some ab- 

 normal activity of the liver cells themselves or to an interference with the 

 normal metabolism of the carbohydrate group. In this latter case it is pos- 

 sible that the usual complete oxidation of carbohydrate is interfered with. 



The well-known disease, diabetes mellitus, in which a large quantity of 

 sugar is persistently excreted daily with the urine, has, doubtless, some close 

 relation to the normal functions of the pancreas. The nature of the relation- 

 ship has not yet been determined, though some recent experiments seem to 

 be pertinent, page 460. 



Mineral Matters, Water, etc. The chief mineral constituents of 

 the foods are sodium, potassium, calcium, magnesium, and iron, together 

 with chlorine, sulphur, and phosphorus. The inorganic substances are not 

 a source of heat. They may supply a certain amount of energy, as osmotic 

 energy, but this is of no significance as compared \vith their influence on the 

 metabolism of organic substances. An animal fed on a normal food de- 

 prived of the mineral constituents survives only a few weeks at most. 



The amount of mineral matter in the tissues of the human body, exclusive 

 of the skeletal parts, is about one per cent. It is safe to say that this is 

 chiefly in complex organic combination in the body. The daily quantity 



