766 DIABETES. [BOOK n. 



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 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 splanchnic nerves. Besides 

 this other nerve-fibres find their way through the sympathetic 

 chain 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 our knowledge is at present imperfect. Some 

 undoubtedly supply the hepatic artery and its branches. 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 to a large extent in the muscular coats of these organs. 

 Others must be regarded as vaso-motor fibres for the branches of 

 the portal vein. Lastly theoretical reasons would lead us to 

 suppose that some are directly connected with the hepatic cells, 

 and observations, so far as they go, tend to support this view. 



467. With regard to the exact nature of the influence 

 started by the puncture of the bulb, and the path by which that 

 influence reaches the liver, our information is at present very 

 imperfect. Seeing how 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. But there is no evidence to shew 

 that the phenomena are brought about either by a loss of tonic 

 vaso-constrictor impulses to and a consequent widening of the 

 hepatic artery or by vaso-motor changes in the portal vein and its 

 branches ; section of both splanchnic nerves, the channels of vaso- 

 constrictor impulses to the liver, does not produce diabetes. Nor 

 is there any valid ground for supposing that the puncture produces 



