CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 745 



called haematoporphyrin) is said to have the composition CLBLN GL 

 differing from bilirubin only in its oxygen and hydrogen (C 32 H 32 N 4 O 6 

 + 2H 2 0-O = C 32 H 36 N 4 6 )*. Moreover in old blood clots in the 

 body the hemoglobin 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 sulpho- 

 cyanide 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 nuclein ( 29) nature, from 

 some of which the iron is more easily removed than others, and 

 these compounds 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 calcu- 

 lated to be set free in the formation out of haemoglobin of the 

 quantity of bilirubin discharged during the same period. Ap- 

 parently 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 some difficulties ; 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 ; and there is no evidence of any sufficient obstruction occur- 

 ring in these cases. Indeed the presence of bilirubin in the urine 



* Doubling the formula for bilirubin given in 245. 



