328 A MANUAL OF PHYSIOLOGY 



blood or tissues.* In mammals life cannot be maintained for any 

 length of time after ligature of the portal vein, since this throws 

 the whole intestinal tract out of gear. But after an artificial 

 communication has been made between the portal and the left 

 renal vein or the inferior cava, the portal may be tied and the 

 animal live for months (Eck). The liver can now be completely 

 removed, but death follows in a few hours. In birds there exists 

 a communicating branch between the portal vein and a vein (the 

 renal-portal) which passes from the posterior portion of the body 

 to the kidney, and there breaks up into capillaries ; and not only 

 may the portal be tied, but the liver may be completely destroyed 

 without immediately killing the animal. In the hours of life that 

 Mill remain to it no accumulation of biliary substances takes place 

 in the blood or tissues. A further indication that bile-pigment is 

 produced in the liver is the fact that the liver contains iron in relative 

 abundance in its cells (p. 382), and eliminates small quantities of iron 

 in its secretion. Now bile-pigment, which contains no iron, is 

 certainly formed from blood-pigment, which is rich in iron, for 

 hsematoidin (Fig. 106), a crystalline derivative of haemoglobin found 

 in old extravasations of blood, especially in the brain, is identical with 

 bilirubin. The seat of formation of bile-pigment must therefore be 

 an organ peculiarly rich in iron. The existence of hsematoidin, 

 however, shows that bile-pigment may, under certain conditions, be 

 formed outside of the hepatic cells. The occurrence of biliverdin 

 In the placenta of the bitch points in the same direction. But the 

 pathological evidence in favour of the pre-formation of the biliary 

 constituents tends rather to shrink than to increase. For many cases 

 of what used to be considered ' idiopathic ' or ' haematogenic ' 

 jaundice, i.e., an accumulation of bile-pigments and bile-acids in the 

 tissues, due to defective elimination by the liver, are now known to 

 be caused by obstruction of the bile-ducts and consequent re-absorp- 

 tion of bile ('obstructive ' or 'hepatogenic ' jaundice). 



But if substances such as the ferments, mucin, hydrochloric 

 acid, the bile-salts and bile-pigments, are undoubtedly manu- 

 factured in the gland-cells, it is different with the water and 

 inorganic salts which form so large a part of every secre- 

 tion. No tissue lacks them ; no physiological process goes 

 on without them ; they are not high and special products. 

 As we breathe nitrogen which we do not need because it is 

 mixed with the oxygen we require, the secreting cell passes 

 through its substance water and salts as a sort of by-play or 



* Wertheimer and Lepage state that bile or bilirubin injected into a bile-duct appears 

 Booner in the urine than in the lymph of the thoracic duct, and therefore conclude that 

 the bloodvessels are the most important channel of absorption. This conclusion, how- 

 ever, cannot be accepted until it is shown that in these experiments the injection did 

 not cause rupture of some of the hepatic capillaries and direct entrance of the bile- 

 pigment into the blood. It is not improbable that the pressure attained by the bile in 

 the bile-capiilaries is a factor in determining the path by which it is absorbed, and that 

 when the pressure rises beyond a certain limit it may pass both into the bloodvessels 

 and into the lymphatics. 



