910 NUTRITION AND HEAT REGULATION. 



entering the splanchnic nerves, proceed to the liver by way of the 

 hepatic plexus and nerves. On this view the center in the medulla 

 constitutes a " sugar-regulating center," which may be acted on 

 reflexly and thus control the process of the conversion of glycogen 

 to sugar. Others have held the view that the effect is exercised 

 indirectly through the adrenal glands. They believe that the 

 sugar puncture results in a reflex stimulation of the adrenal 

 glands, whereby more epinephrin is thrown into the circulation, 

 and that the increase in glycogenolysis is due to the action of the 

 epinephrin on the liver cells. Recent experiments do not support 

 wholly either one of these views, but indicate rather that while the 

 nerve-fibers involved act directly upon the liver cells the presence 

 of the adrenal glands is in some way necessary for the reaction.* 

 Just how this mechanism acts under normal conditions cannot, 

 therefore, be determined. It is known, however, that under condi- 

 tions of emotional excitement or nervous stress glycosuria is apt to 

 occur, and the explanation usually offered is that the secretion of 

 the adrenals is increased by reflex stimulation with a resulting in- 

 crease in sugar output from the liver. In both of these possibilities, 

 a reflex stimulation of the hepatic nerves or of the adrenal glands, 

 there is a break down in the completeness of the regulation which 

 affects chiefly the process of glycogenolysis. In this connection 

 we may recall also the severe form of glycosuria following upon 

 removal of the pancreas, the so-called pancreatic diabetes (p. 887). 

 Here also the trouble is referable to a change in one of the internal 

 secretions, but in this instance it is a defective rather than an ex- 

 cessive secretion which induces the glycosuria. Whether the loss of 

 the internal secretion of the pancreas affects the stage of glycogenol- 

 ysis or the stage of glycolysis is perhaps an open question. The 

 usual view has been that this secretion is concerned somehow with 

 the processes of consumption of sugar in the tissues, but in what way 

 it enters into this process remains to be discovered. 



In mankind defective sugar metabolism manifests itself chiefly 

 in the disease known as diabetes mellitus. In this severe and usually 

 fatal disease the amount of sugar lost daily in the urine may be very 

 large. In severe forms of the disease practically all the carbohydrate 

 of the food may be excreted in the urine in the form of sugar, 

 and even when the carbohydrate in the diet is eliminated com- 

 pletely, sugar continues to be secreted in the urine in consider- 

 able amounts. In these latter cases the sugar is supposed usually to 

 have its source in the proteins of the food or of the body, a view 

 which is supported by the fact that the amount of nitrogen and dex- 

 trose excreted in the urine may exhibit a constant proportion to each 



* For review and literature consult Macleod, Harvey Lecture, "Journal of 

 the American Medical Association," April 18, 1914. 



