286 BLOOD-PRESSURE AND BILE SECRETION. [BOOK II. 



the tide of blood through the liver would ebb and flow according to 

 the absence or presence of food in the alimentary canal 1 .' 



That the increase in the pressure of blood in the portal vein 

 would ipso facto lead to increase in the secretion of bile, cor- 

 responding doubtless to a general increase in all the activities of the 

 liver, appears to be proved by a variety of facts. Thus when the 

 general arterial pressure is very greatly lowered by blood-letting the 

 flow of bile is diminished 2 , though Heidenhain's own experiments 

 shew that, as a result of haemorrhage, the pressure in the carotid 

 may fall to one-half its initial value without a change in the rate of 

 the flow of bile being noticeable 3 . 



Section of the spinal cord in the cervical region leads to a great 

 fall in the amount of the bile secreted, which is concomitant with the 

 general fall of pressure throughout the vascular system. Stimulation 

 of the spinal cord, whether direct or reflexly induced by stimulation 

 of sensory nerves, leads to a diminished flow of bile by the contrac- 

 tion which it occasions in the vascular areas which receive their 

 nervous supply through the splanchnic nerves, and of which a conse- 

 quence is a diminished flow of blood through the portal vein 

 (Lichtheim 4 , Heidenhain 5 ). Section of the splanchnic nerves, which 

 is followed by a dilatation of all the arteries which furnish the 

 blood to the radicles of the portal vein, leads to an increase in the 

 flow of bile (Heidenhain). On the other hand, stimulation of the 

 splanchnic nerves by causing a constriction of the arteries, and a con- 

 sequent slowing of the portal stream, is followed by a diminution in 

 the flow of bile (Munk 6 ). 



The stimulation of various nerves has thus an influence on the 

 secretion of bile ; this influence is, however, only an indirect one, 

 through the variations which the stimulation occasions in the flow of 

 blood through the liver. No evidence exists which points to the 

 existence of any nervous apparatus, local or central, directly control- 

 ling the secretion of bile. 



The Pressure under which the Bile is secreted. 



In the case of the saliva, reference was made to the fact that 

 it may be secreted though the pressure exerted by the secreted fluid 

 is considerably higher than that of the blood circulating through the 

 arteries which supply the gland a fact which conclusively proves 

 that the secretion is not an act of filtration. The secretion of the 

 bile takes place under a pressure which, compared with that of the 



1 M. Foster, A Text-Book of Physiology. Fifth ed. Part n. (1889), p. 436. 



2 Korner und Strube, Studien des physiologischen Institute zu Breslau, u. (1863), 

 p. 101. 



3 Heidenhain, Gallenabsonderung,' Hermann's Handbuch, Vol. v. i. p. 263. 



4 Lichtheim, ' Ueber den Einfluss der Ruckenmarksreizung auf die Gallen- 

 absonderung,' Inaug. Diss. Berl. 1867 (quoted by Heidenhain). 



5 Heidenhain, Studien d. physioL Inst. zu Breslau iv. (1868), p. 226. 



6 J. Munk, 'Ueber den Einfluss sensibler Reizung auf die Gallenausscheidung,' 

 Pfliiger's Archiv, Vol. vm. (1874), p. 151. 



