THE SECRETION OF THE DIGESTIVE JUICES 385 



(Eck). The liver can- now be completely removed, but death 

 follows in a few hours. A good method of establishing an- Eck's 

 fistula i's to make a longitudinal incision in the inferior vena cava 

 and the portal or superior mesenteric vein, and to suture the edges 

 of the two openings together with a very fine sewing-needle and 

 thread (Carrel and Guthrie). 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 immedi- 

 ately killing the animal. In the hours of life that still remain to it 

 no accumulation of biliary substances (acids or pigments) takes* 

 place in the blood or tissues. A further indication that bile-pig- 

 ment is produced in the liver is the fact that the liver contains 

 iron in relative abundance in its cells (p. 21), and eliminates small 

 quantities of iron in its secretion. Now, bile-pigment, which con- 

 tains no iron, is certainly formed from blood-pigment, which is rich 

 in iron. For haematin, when injected under the skin, has been found 

 to appear almost quantitatively in the form of bile-pigment in the 

 bile, and haematoidin (Fig. 159), a crystalline 

 derivative of haemoglobin found in old ex- 

 travasations of blood, especially in the brain 

 and in the corpus luteum, is identical with 

 bilirubin. The fact that one of the derivatives 

 of haematin, haematoporphyrin (C 33 H 38 N 4 O 6 ), 

 contains no iron, and is probably nearly 



related to bilirubin (C 32 H 36 N 4 O 6 ), suggests 



that haematoporphyrin may be an inter- pig I59 Z^ raat oidin. 

 mediate step in the formation of bile-pigment 



from blood- pigment. In any case, the seat of formation of bile- 

 pigment might be expected to be an organ peculiarly rich in iron. 

 The existence of haematoidin, 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 accumu- 

 lation 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-absorption of bile (' obstructive ' 

 or ' hepatogenic ' jaundice). 



But if substances such as the ferments, mucin, hydrochloric acid, 

 the bile-salts and bile-pigments, are undoubtedly manufactured in the 

 gland-cells, it is different with the water and inorganic salts which 

 form so large a part of every secretion. No tissue lacks them ; no 



2 5 



