THE HISTORY OF GLYCOGEN. 449 



viously starved so that the liver contains little or no glycogen, the urine 

 will, after the operation, contain little or no sugar. It is clear thut the 

 urinary sugar of this form of artificial diabetes comes from the glyeogen 

 of the liver. The puncture of the medulla causes such a change in the 

 liver that the previously stored-up glycogen disappears, and the blood 

 becomes loaded with sugar, much, if not all, of which passes away by 

 the urine. In the absence of any proof to the contrary, we may assume 

 that in this form of artificial diabetes, the glycogen previously present 

 in the liver becomes converted into sugar, just as we know that it does 

 become so converted by post-mortem changes. The glycogenic function 

 of the liver is, therefore, subject to the influences of the nervous system, and, 

 in particular, to the influence of a region of the cerebro-spinal centre, which 

 we already know as the vasomotor centre, or at least of a part of that region. 



Before we attempt to discuss this nervous influence we must say a few 

 words on the nerves of the liver. 



386. The liver is supplied with nerves from the hepatic plexus, which 

 passes into the liver at the porta and, running in the portal canal with the 

 hepatic artery and portal vein, is distributed to various parts of the organ. 

 This plexus, which is the only nerve supplying the liver, consists partly of 

 medullated and partly of non-medullated fibres, and is an extension of the 

 great solar plexus, already often mentioned. Into that plexus, as we have 

 already seen, the right (posterior) vagus sends the greater part of its fibres, 

 and in that plexus both the abdominal splanchnic nerves, major and minor, 

 end, on both sides of the body. The left (anterior) vagus forms slight con- 

 nections only with the solar plexus, but sends off a very distinct branch 

 directly to the hepatic plexus. The liver, therefore, has nervous connec- 

 tion with the central nervous system by both vagus nerves and by the 

 (abdominal) splanchnic nerves. Besides this, other nerve-fibres find their 

 way through the splanchnic sympathetic chain, or possibly otherwise, to 

 the solar plexus from the spinal cord without taking part in either of the 

 splanchnic nerves ; and these may, perhaps, join the hepatic plexus. 



Concerning the destination of the fibres of the hepatic plexus within 

 the liver we know little or nothing definitely. Some, undoubtedly, supply 

 the hepatic artery and its branches ; but we cannot at present say what 

 proportion of the whole number of fibres end in this way. Some, again, 

 are destined for the bile-ducts, and before the plexus passes into the liver 

 it sends fibres to the gall-bladder ; these probably end in the muscular 

 coats of these organs. Whether any of the nerve-fibres end in the re- 

 markably muscular coats of the portal vein, or whether, as theoretical 

 reasons would, perhaps, lead us to suppose, some are connected with the 

 hepatic cells, we do not for certain know, though some observers have 

 claimed to have traced nerve-fibres directly into the hepatic cells. 



387. With regard to the exact nature of the influence started by the 

 puncture of the medulla, and the path by which that influence reaches the 

 liver, our information is at present very imperfect. One thing seems clear, 

 viz., that the influence in 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 how close to, or almost indentical with, the vaso- 

 motor centre is the diabetic centre, if we may use the phrase, it seems nat- 

 ural to suppose that the undue conversion of glycogen into sugar which 

 follows the puncture is the result of some vasomotor disturbance in the 

 liver, for instance, dilatation of the hepatic artery. But we have no clear 

 proof that this is the true explanation. 



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