548 METABOLISM, NUTRITION AND DIETETICS 



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. 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 

 into dextrose in the liver, there is no evidence that the amount of the 

 enzyme which hydrolyses the glycpgen is increased. Whether the 

 action of the enzyme is favoured in some other way e.g., by the 

 production of a co-ferment or by some change in the condition of 

 the glycogen which renders it more open to attack is unknown. 



Certain facts have recently been brought forward which go to 

 show that the action of the splanchnic fibres on the liver is not 

 a direct action, but that in some way or other the concomitant 

 activity of the adrenal glands is essential. For if the adrenals have 

 been previously extirpated, the puncture does not cause glycosuria. 

 It was at first thought that the reason for this was that the removal 

 of - the adrenals is itself followed by the disappearance of glycogen 

 from the liver, and, as has been pointed out, the presence of glycogen 

 in the liver is essential to the success of the puncture experiment. 

 The matter, however, is not so simple. For although in certain 

 animals e.g., the dog the liver does lose all its glycogen when the 

 adrenals have been taken away, this is not the case in the rabbit, 



