438 HAN'DUOOK OF PHYSIOLOGY. 



stimulus cannot be traced to the liver, but, at any rate, it is not con- 

 ducted by the vagi or by the splanchnics, but at first it passes from the 

 lower part of the floor of the fourth ventricle and medulla down the 

 spinal cord as far as in rabbits the fourth dorsal vertebra, and hence 

 to the first thoracic ganglion. The formation of sugar by the liver is 

 also not a vaso-dilator effect, since it will occur when the vessels are 

 constricted. 



Many other circumstances will cause glycosuria. It has been observed 

 after the administration of various drugs e.g. , strychnine (in frogs), 

 phloridzin, a glucoside, and phloretin, a derivative of phloridzin, not a 

 glucoside, morphine, nitrite of amyl, etc. after the injection of urari, 

 poisoning with carbonic oxide gas, the inhalation of ether, chloroform, 

 etc., the injection of oxygenated blood into the portal venous system. 

 It has been observed in man after injuries to the head, and in the course 

 of various diseases. 



In all such cases, at any rate, the glycosuria appears to be due to some 

 abnormal activity of the liver cells themselves set up by the direct action 

 of the secretory nerves upon them. 



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

 sugar is persistently secreted daily with the urine, has, doubtless, some 

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

 the relationship has not yet been determined, though some recent experi- 

 ments seem to be pertinent (see p. 318). 



Effect of too much Food. All the three classes of food-stuffs men- 

 tioned fats, carbohydrates, and gelatin have their distinct uses when 

 combined with proteids. A small amount of fat or a larger amount of 

 carbohydrate (starch or sugar) added to some proteid diminishes the 

 amount of proteid required before nitrogenous equilibrium is attained 

 (in a dog to the extent of 50 per cent or more), but if the carbohydrate 

 exceed a certain minimum it is retained in the body as fat.* If the pro- 

 teid be increased, the metabolism is increased likewise, and so fat may 

 not be deposited, even if the carbohydrate of the diet be excessive. It 

 is even possible that some of the already stored-up fat may be used up, 

 and so loss of weight (fat) might result. 



Persistent excess of carbohydrate food produces an accumulation of 

 fat, which may not only be an inconvenience causing obesity, but may 

 interfere with the proper nutrition of muscles, and a feebleness of the 

 action of the heart, with other troubles. Starches when taken in great 



*The result of various feeding experiments, e.g., of the milch cow fed upon 

 grass, have proved beyond all doubt that fat is formed by the tissues chiefly from 

 carbohydrate food, but to a less extent from proteids. Fatty foods, even if they 

 indirectly lead to the deposition of fats, are not as such deposited in the tissues. 

 Fat is everywhere in the body an effect of actual protoplasmic metabolism. 



