METABOLISM OF CARBO-HYDRATES GLYCOSURI AS 539 



is made. But sometimes these operations are themselves followed 

 by temporary glycosuria, due, it is believed, to irritation of the 

 same efferent nervous path whose elimination when the splanchnics 

 are divided prevents the glycosuria. /"The simplest explanation of 

 the phenomena is that a ' sugar centre ' that is to say, a centre 

 which has the important office of regulating the sugar content of the 

 blood by governing the rate at which glycogen* is built up and de- 

 composed in the liver, as the salivary centre regulates the rate at 

 which the constituents of saliva are formed and discharged has 

 been injured or irritated by the puncture/ If a nervous centre does 

 in fact preside over this internal secretion of the liver, it will, of 

 course, be connected with efferent and afferent nerves. The former, 

 as denned by the experiments alluded to, seem to be confined to 

 the splanchnic nerves; the latter are believed to run especially, 

 though not exclusively, in the vagus. Section of the vagi has no 

 effect either in causing glycosuria of itself or in preventing the 

 ' puncture ' glycosuria, but stimulation of the central ends of these 

 and of other afferent nerves may cause sugar to appear in the 

 urine, although not, it is said, if precautions are taken to prevent 

 any degree of asphyxia. ; ' Asphyxia produces an increase in the 

 sugar content of the blood, an increase in the flow of urine and 

 glycosuria. ) 



It has usually been assumed that this action of asphyxia is due to 

 the effect upon the centre of blood over-rich in carbon dioxide (and 

 other metabolic products) or impoverished as regards oxygen. But 

 there is some evidence that the altered blood may also affect the 

 liver-cells directly, or, what comes to the same thing in the long-run, 

 that interference with the internal respiration of the hepatic tissue, 

 operating, it may be, through an increase in the concentration of the 

 hydrogen ions, upsets the equilibrium of those intracellular reactions 

 by which glycogen is formed from dextrose and dextrose from 

 glycogen. In like manner it may be supposed that under normal 

 conditions the rate of transformation of the hepatic glycogen into 

 dextrose is adjusted to the dextrose content of the blood, not only 

 by reflex nervous impulses passing through the sugar-regulating 

 centre, but also by the direct influence of the dextrose itself circu- 

 lating in the blood, upon whose concentration the reaction of the 

 centre on the one hand and of the liver-cells on the other may in 

 part depend, f So that when the proportion of sugar in the blood 

 tends to sink we may perhaps picture the centre as sending impulses 

 to the liver which increase the rate at which the glycogen is hydro- 

 lysed ; and when the proportion tends to rise, we may think of it as 

 sending impulses which inhibit the hydrolysis, both effects being 

 accentuated by the direct influence of the changes of concen- 

 tration on the hepatic cells/ Whatever the mechanism may be 

 through which the puncture hastens the transformation of glycogen 



