370 BLOOD-SUPPLY OF LIVER. ^BOOK n. 



pressure in the portal system ; and in the dog it has been found 

 that while the pressure of the bile secreted stood at about 200 mm. 

 of a solution of sodium carbonate, that is, about 15 mm. mer- 

 cury, the blood-pressure in a branch of the superior mesenteric 

 vein stood only at about 90 mm. of the same solution, that is, 

 about 7 mm. mercury. Now the venous pressure in the mesen- 

 teric veins is higher, though only slightly higher, than that in the 

 portal vein into which these pour their blood (the difference of 

 pressure being the main cause why the blood Hows from the one 

 into the other), and is therefore certainly higher than the pies- 

 sure in the portal capillaries of the hepatic lobules. So that what 

 is true of the salivary gland is also true, on a different scale, of 

 the liver, viz. that the pressure exerted by the secretion is higher 

 than the pressure of the blood in the vessels feeding the secreting 

 cells. 



217. If the pressure in the bile duct be artificially increased, 

 as by pouring fluid into the glass tube or manometer with which 

 the cannula in the duct is connected, a resorption of the secreted 

 tile takes place ; and resorption will also take place within the 

 body, when the pressure generated by the act of secretion itself 

 reaches and is maintained at a sufficiently high level. Thus 

 when in the living body the bile duct is ligatured, or becomes 

 obstructed by gallstones or otherwise, fluid is accumulated on the 

 near side of the ligature at a pressure which goes on increasing 

 until resorption of bile takes place, bile salts and biliary pigments 

 are thrown back upon the system, and "jaundice" results. It 

 would appear that in these cases resorption takes place through 

 the interlobular bile ducts and not through the hepatic cells or 

 other structures within the lobules. The high pressure in the 

 ducts does not lead to a reversal of the current in the hepatic 

 cells (at most it slackens or possibly stops the current) but the 

 bile secreted into the interlobular ducts escapes from these. It 

 further appears that the escape is not into the blood vessels but 

 into the lymphatics ; the bile salts, pigments and other constitu- 

 ents are carried into the thoracic duct, and in an indirect manner 

 only find their way into the blood stream. 



To complete the history of the secretion of bile we ought now 

 to turn to the manufacture of the biliary constituents within the 

 cells. But since the hepatic cells are also engaged in labours 

 other and more important perhaps than that of secreting bile, it 

 will be convenient to defer what we have to say on this point 

 until we come to speak of the formation of glycogen and of the 

 general metabolic events taking place in the liver. 



