SEC. 4. THE FORMATION OF THE CONSTITUENTS 



OF BILE. 



477. Bile Pigments. After extirpation of the liver no 

 accumulation of bile pigment or bile salts takes place in the blood. 

 This is well shewn in frogs, which survive the operation for some 

 considerable time ; but the same results have been obtained in 

 birds (geese and ducks). There can be no doubt therefore that 

 these substances are formed in the liver and not simply withdrawn 

 from the blood by the liver in some such way as we have seen 

 reason to think urea is withdrawn from the blood by the kidney. 



When the plasma of circulating blood is made to contain 

 haemoglobin detached from the corpuscles, bile pigment frequently 

 makes its appearance in the urine. The presence of free haemo- 

 globin may be obtained by injecting into the veins a solution 

 of haemoglobin or blood made 'laky' by freezing and thawing 

 or by the addition of a small quantity of bile salts, or by simply 

 injecting into the veins a quantity of distilled water or a small 

 quantity of ether or chloroform or of bile salts, all of which tend 

 to ' break up ' red corpuscles and set free haemoglobin. A similar 

 result occurs in poisoning by certain drugs, such as toluylen- 

 diamine. Under these circumstances not only does bile pigment, 

 bilirubin, make its appearance in the urine, but the quantity of 

 bilirubin secreted by the liver is increased. Obviously the presence 

 of dissolved haemoglobin in the plasma of the blood, and, pre- 

 sumably more especially of the blood reaching the liver by the 

 portal vein, leads to an increased formation of bilirubin, which 

 takes place in such a manner that the whole of the bilirubin 

 so formed does not pass into the bile but part is retained in or 

 thrown back into the circulation and appears in the urine. 



We have already mentioned the chemical connection between 

 haemoglobin and bilirubin. Haemoglobin, after the detachment 

 of its proteid component becomes haematin (C 32 H 32 N 4 Fe0 4 ). By 

 treatment with sulphuric acid or otherwise ( 351), hsematin may 

 be deprived of its iron; and this iron-free haematin (sometimes 



