822 NUTRITION AND HEAT REGULATION. 



tion is of the greatest importance to the body, since any distinct 

 increase in the percentage of dextrose in the blood, a condition 

 known as hyperglycemia, is followed promptly by glycosuria, that 

 is, the appearance of sugar in the urine. It has been suggested 

 that the regulation of the output of sugar from the liver is con- 

 trolled reflexly through the nervous system. Some evidence for 

 this view is found in the following facts: Bernard discovered (1855) 

 that a puncture of the medulla, made between the levels of origin 

 of the vagus and auditory nerves, causes the development of a 

 condition of glycosuria. This puncture, known as the "piqure" 

 or "sugar puncture," fails to cause glycosuria if the animal has been 

 starved previously so as to remove most of the glycogen from the 

 liver or if the splanchnic nerves have been cut. Moreover, stimula- 

 tion of various sensory nerve trunks, the vagus, for example, causes 

 the same phenomenon, and in human beings lesions of the central 

 nervous system may likewise develop a condition of glycosuria. 

 These results have been explained in two ways. The puncture or 

 sensory stimulation may act upon the vasomotor center of the 

 medulla, cause a dilatation of the blood-vessels in the liver, and 

 thus indirectly accelerate the output of sugar; or these stimuli may 

 act upon a distinct sugar-regulating center and through it augment 

 directly the conversion of glycogen to sugar in the liver. According 

 to this latter view the efferent fibers for the center reach the liver 

 via the splanchnic nerves. If such a nervous mechanism exists 

 it affords a suitable means for the adjustment of the supply of 

 sugar to the needs of the tissues, particularly the muscles. The 

 contractions of the muscles and the heart by exciting their contained 

 sensory fibers might be supposed to stimulate reflexly the sugar 

 center and thus provide an increased output of sugar in proportion 

 to the extent of the contractions (Pfluger). While this theory is 

 attractive, it has not yet received definite experimental proof. 

 It is certain, however, that by some means, chemical or nervous, 

 the supply of sugar from the liver is regulated, and that under 

 various unusual and pathological conditions this regulation is 

 broken down with the production of conditions of hyperglycemia 

 and glycosuria. It is interesting, from a physiological standpoint, 

 to recall that glycosuria may result temporarily from too great 

 an ingestion of carbohydrate food (see Alimentary Glycosuria, 

 p. 735). The liver in this case gets more sugar than it can convert 

 to glycogen, and an excess gets through into the general circulation. 

 From a medical standpoint most interest attaches to the cases of 

 glycosuria occurring under pathological and experimental con- 

 ditions. 



Pancreatic Diabetes. Some of the facts regarding this form 

 of diabetes are described on p. 755. The immediate cause of 



