CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 781 



porphyrin, is said to have the composition C 32 H 32 N 4 O 5 , differing 

 from bilirubin only in its oxygen and hydrogen (C 32 H 32 N 4 O 5 

 + 2H 2 O - = C 32 H 36 N 4 6 ). Moreover in old blood clots in the 

 body the haemoglobin of the clot becomes in time transformed 

 into an iron- free body which has been called haematoidin, but 

 which both in composition and in reactions appears to be identical 

 with bilirubin. 



These several facts lead us to the conclusion that the bilirubin 

 of the bile is simply some of the haemoglobin of the blood trans- 

 formed by the throwing off of its proteid and its iron components. 

 It is natural to suppose that the transformation takes place in 

 and is effected by the agency of the hepatic cells ; and this view 

 is supported by the fact that the hepatic cells are characterized by 

 containing certain peculiar iron compounds. When all the blood 

 is carefully washed out of the liver by injection through the blood 

 vessels, by which means the remaining bile is got rid of at the 

 same time, the hepatic substance is found to contain a small 

 quantity of iron, sufficient to give the cells a diffused dark colour 

 when treated with ammonium sulphide ; the exact amount appears 

 to vary largely, but the causes of the variation have not been 

 determined. That this iron is in organic combination is indicated 

 by the fact that with potassium ferrocyanide and sulphocyanide 

 the blue or red reaction is not observed until after treatment with 

 hydrochloric acid. Apparently there are several such compounds, 

 of a proteid or of a nucleo-albumin (29) nature, from some of 

 which the iron is more easily removed than others, and these com- 

 pounds appear to be present in both the cell-substance and the 

 nucleus. It will be remembered ( 244) that bile contains a 

 distinct quantity of iron, which probably has its origin in the iron 

 thus set free from haemoglobin and retained in the hepatic cell ; 

 but it does not follow that all the iron thus set free makes its way 

 into the bile ; and indeed the quantity of iron discharged in the 

 bile in 24 hours is much smaller than the quantity calculated to 

 be set free in the formation out of haemoglobin of the quantity of 

 bilirubin discharged during the same period. Apparently the iron 

 compounds of the hepatic cell have some other work than the 

 simple discharge of iron into the bile. 



The fact mentioned above, that the presence of free haemoglobin 

 in the blood leads not only to an increase of bilirubin in the bile, 

 but also to its presence in the urine, offers a difficulty ; for if the 

 bilirubin be formed out of haemoglobin by and in the hepatic cell, 

 one would expect to find that the whole of it passed into the bile, 

 and that it could not appear in the blood and so in the urine 

 unless reabsorption from the bile passages, due to obstruction, 

 took place. Indeed the presence of bilirubin in the urine in these 

 cases has been urged by some as an argument that bilirubin is 

 formed in the .blood or at least elsewhere than in the liver and 

 is simply excreted by the liver. Not only however is there, as 



