732 DIABETES. [BOOK n. 



-.question is not carried down by the main vagus trunks; for not 

 only has the section of both these nerves in the neck no marked 

 effect in the way of producing diabetes ; but the ' diabetic punc- 

 ture ' of the medulla oblongata is as efficient after division of 

 both vagus nerves as before. Seeing ho\v close to or almost 

 identical with the vaso-motor centre is the diabetic centre if we 

 may use the phrase, it seems natural to suppose that the undue 

 conversion of glycogen into sugar which follows the puncture is 

 * the result of some vaso-motor disturbance in the liver, for instance 

 dilation of the hepatic artery. But we have no clear proof that 

 this is the true explanation, and indeed if the phenomena are the 

 result of the failure of normal vasoconstrictor impulses, those 

 impulses do not reach the liver by the tract which we should 

 suppose them naturally to take, viz. from the vaso-constrictor 

 region of the cord through the splanchnic nerves, for division of 

 the splanchnic nerves even on both sides does not cause diabetes. 

 Moreover that the effects are not due to vaso-dilator results is 

 shewn by the fact that strychnia poisoning produces diabetes in 

 frogs, and produces it by rapidly hurrying into sugar the hepatic 

 store of glycogen. Now in strychnia poisoning the blood vessels 

 are constricted, not dilated, their muscular fibres like the skeletal 

 muscles being thrown into contraction by the action of the poison. 



The vascular relations of the liver are it is true peculiar, the 

 small hepatic artery contrasting with the wide portal vein ; and it 

 may be that the diabetic effects are contingent not so much on 

 the absolute account of constriction or dilation of the hepatic 

 arteryjCas on the relation of the flow through that artery to the 

 flow through the portal vein. Indeed in support of this view may 

 be adduced the statement that section of both splanchnic nerves 

 not only does not cause diabetes but prevents the usual effects of 

 the diabetic puncture ; and this has been interpreted as shewing 

 that the increased portal flow thus induced counterbalances the 

 effects of dilation of the hepatic artery. But we have at present 

 no exact information, and there is as yet nothing distinctly to 

 inegative the view that in this artificial diabetes the nervous 

 influence is brought to bear on the hepatic cell itself. 



There are some facts which seem to shew that the path of 

 this nervous influence on its way to the liver from the spinal 

 cord passes through the first thoracic ganglion, ganglion stellatum ; 

 but how it reaches the hepatic plexus from this ganglion is wholly 

 unknown. 



468. A temporary diabetes may 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, 



