CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 767 



its effect by disturbing the balance between the arterial blood- 

 supply by the hepatic artery and the venous supply by the portal 

 vein. It seems more probable that the nervous events taking 

 place in the spinal bulb by reason of the puncture are able in 

 some way or other to bring about changes in the hepatic cells 

 themselves ; but, though it is stated that stimulation of the nerves 

 going to the liver causes an increase of sugar in the blood of the 

 hepatic vein, and this may be taken as an indication that the nervous 

 impulses have stirred up the hepatic cells to an unwonted pro- 

 duction of sugar, we have as yet no satisfactory evidence in favour 

 of this view. It has been suggested that the area in the spinal 

 bulb acts as an inhibitory centre in regard to the sugar-producing 

 activity of the hepatic cells, and that the effect of the puncture is 

 the result of the failure of this inhibitory influence and not the 

 result of positive exciting impulses ; but this as yet remains to be 

 proved. 



Nor can anything very definite be at present said concerning 

 the path by which the influence, whatever be its nature, started 

 by the puncture travels from the bulb to the liver. It does not 

 travel by the vagus nerves, for the puncture is effective after 

 division of both vagus nerves. It probably makes its way by the 

 sympathetic system, passing into the sympathetic chain, in the 

 upper thoracic region, and if it be true as stated that the puncture 

 fails if both splanchnic nerves be divided, eventually travelling 

 along those nerves. 



A temporary diabetes may also be brought about by the 

 administration of the substance phloridzin. This however is a 

 glucoside, and part of the sugar which appears in the urine, after 

 a dose of it, may come direct from the drug itself; but the 

 quantity of sugar discharged is too great to be accounted for in 

 this way, and similar diabetic effects are produced by the admini- 

 stration of phloretin, a derivate of phloridzin, not a glucoside, 

 and not giving rise to sugar by its own decomposition. The exact 

 manner in which phloridzin thus produces diabetes has been and 

 is a matter of much dispute. It certainly is not by simply hurry- 

 ing into sugar the hepatic store of glycogen ; the diabetes may be 

 produced in a starving animal whose liver may be presumed to be 

 free from glycogen, and indeed in an animal the liver of which has 

 been removed. And it seems further probable that the action of 

 the drug affords an instance ( 461) of the formation of sugar 

 through proteid metabolism. 



Artificial diabetes is also a prominent symptom of urari poison- 

 ing. This is not due to the artificial respiration, which is had 

 recourse to in order to keep the urarised animals alive; because, 

 though disturbance of the respiratory functions sufficient to inter- 

 fere with the hepatic circulation may produce sugar in the urine, 

 artificial respiration may with care be carried on without any 

 sugar making its appearance. Moreover, urari causes diabetes in 



