464 BLOOD-SUPPLY OF LIVER. [BOOK n. 



supply through the portal vein is accompanied by a corresponding 

 increase of the lesser supply of arterial blood through the hepatic 

 artery, is not known. 



255. It is interesting to observe that the pressure under 

 which the bile is secreted is relatively low like that of the 

 pancreatic juice, not high like that of the saliva; it is much lower 

 than the arterial pressure in the same animal, whereas in the case 

 of saliva ( 227) the pressure is greater than the blood-pressure in 

 the carotid artery. But, in the case of bile, since the blood which 

 flows through the hepatic lobules is, mainly, venous portal blood, 

 we have to compare the pressure of the secretion not with arterial 

 pressure but with the venous 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. mercury, 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 mesenteric 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 flows from the one into the other), and is therefore certainly 

 higher than the pressure 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. 



256. 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 

 bile 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 

 constituents 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 



