SEC. 3. THE FORMATION OF THE CONSTITUENTS 



OF BILE. 



375. 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 simply withdrawn from the blood by the liver in some such way 

 as we have seen reason to think urea is withdrawn from the 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 fre- 

 quently makes its appearance in the urine. The presence of free 

 haemoglobin may be secured by injecting into 'the veins a solu- 

 tion of haemoglobin or blood made 4 laky ' by freezing and thaw- 

 ing 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 jn poisoning by certain drugs, such as 

 toluylendiamine. 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. Obvi- 

 ously the presence of dissolved haemoglobin in the plasma of 

 the blood, and, presumably 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 FeO 4 ). By 

 treatment with sulphuric acid or otherwise ( 282), haematin 

 may be deprived of its iron ; and this iron-free haa matin (some- 



584 



