460 THE SECRETION OF BILE. [BOOK n. 



and is especially influenced by food ; it is seen to rise rapidly after 

 meals, reaching its maximum, in dogs, in from four to eight hours. 

 There seems to be an immediate, sudden rise when food is taken, 

 then a fall, followed subsequently by a more gradual rise up to 

 the maximum, and ending in a final fall to the lowest point. 

 The curve of secretion, in fact, resembles that of the secretion of 

 pancreatic juice in having a double rise ; and as in that case so 

 in this, it is very probable that the first rise is in part the result 

 of nervous action, and it is also possible that nervous influences 

 intervene in the second more lasting rise; but, as we shall see 

 presently, even nervous influences may affect the liver in a very 

 indirect manner, and our knowledge as to any direct action of the 

 nervous system on the liver is at present very imperfect. 



The liver receives its chief nervous supply from the solar 

 plexus, and to a great extent through that part of the solar 

 plexus called the hepatic plexus which embraces the portal vein, 

 hepatic artery and bile duct, as these plunge into the liver 

 at the porta. The solar plexus is fed by the two splanchnic 

 nerves, major and minor, as well as by other smaller nerves from 

 the lower parts of the sympathetic chain, and by the terminal 

 portion of the right vagus nerve. Small branches from the left 

 vagus, rami hepatici, also pass directly to the liver from the 

 terminations of that nerve on the stomach, finding their way also 

 through the porta. The fibres thus entering the liver from the 

 several sources are, for the most part, non-medullated fibres ; with 

 these, however, are mixed a certain number of medullated fibres. 



As to the functions of these nerves in reference to the secretion 

 of bile, we may say at once that no satisfactory or exact statement 

 can at present be made. 



It must be remembered, however, that the liver is so peculiarly 

 related to the other organs of digestion, and its vascular arrange- 

 ments so special that, with regard to it, as compared with many 

 other organs, an intrinsic nervous mechanism must occupy a more 

 or less subordinate position. The blood-supply of the pancreas 

 for instance is dependent chiefly on the width for the time being 

 of the pancreatic arteries; it will be affected of course by the 

 general arterial pressure as well as by any circumstances which 

 affect the outflow by the pancreatic veins, and therefore by the 

 condition of the portal venous system of which those veins form a 

 part ; but in the main, the amount of blood bathing the alveoli of 

 the pancreas will depend on whether the pancreatic arteries are 

 constricted or dilated. The quality of the blood reaching the 

 pancreas, being arterial blood drawn direct from the arterial 

 foundation, will be modified only by such circumstances as modify 

 the general mass of the blood. 



Very different is the case of the liver. The supply of arterial 

 blood coming direct through the hepatic artery is small compared 

 with the mass pouring through the vena portse ; this arterial blood 



