CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 731 



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 influence of the nervous system, and in particular to the 

 influence of a region of the cerebro-spinal centre which we already 

 know as the vaso-motor 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. 



466. 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 supply to 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 connections only with the solar 

 plexus but sends off a very distinct branch directly to the hepatic 

 plexus. The liver therefore has nervous connection 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 remarkably 

 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. 



467. 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 



