580 FORMATION OF BILIRUBIN. [Book n. 



haemoglobin from the red corpuscles as these are streaming 

 slowly through the lobular hepatic capillaries in close contact 

 with the hepatic cells? Now, as far as we know at present, 

 haemoglobin can only be set free by means of a disintegration 

 of the corpuscles ; we have no instances of a corpuscle parting 

 with some of its haemoglobin and proceeding on its way other- 

 wise unchanged ; and we have no histological evidence of any 

 disintegration of red corpuscles in the liver corresponding to 

 the formation of bile. Nor can we draw any conclusion from the 

 results of a comparative enumeration of red corpuscles in the 

 portal and hepatic blood, for these are too insecure to rest any 

 conclusion upon. On the other hand, as we have just seen, 

 the presence in the plasma of the blood of haemoglobin in a free 

 condition is peculiarly potent in exciting the formation of bili- 

 rubin. The evidence therefore is very strong for the view that, 

 as far as the formation of the greater part at least of the biliru- 

 bin is concerned, the action of the hepatic cell is limited to 

 converting into bilirubin the free haemoglobin offered to it by 

 the portal blood. 



By what means, under normal conditions, is the presence of 

 that free haemoglobin secured ? We have seen reason (§ 373) 

 to conclude from histological appearances that a certain number 

 of red corpuscles undergo change in the spleen pulp ; and it 

 seems natural to infer that one duty of the spleen is to set free 

 haemoglobin from the corpuscles and thus, through the splenic 

 veins and so the portal vein, to supply the liver with material 

 for bilirubin. But this cannot be the only source, since the 

 secretion of bile continues after extirpation of the spleen. 

 There must therefore be other regions of the body in which a 

 similar change of red corpuscles is going on ; it has been sug- 

 gested that the red marrow of bones is one of these ; but further 

 information on these points is needed. 



We may then go so far as to say that the bilirubin of the 

 bile is derived from the haemoglobin of the blood, and that the 

 later stages of the transformation, including the discharge of 

 the iron of the haematin component, take place in and by means 

 of the hepatic cell ; but much be} r ond this is at present uncer- 

 tain. It must be remembered too that, though after extirpation 

 of the liver no accumulation of bilirubin takes place, shewing 

 that the bilirubin is formed by the liver and not elsewhere ; yet 

 the whole change from red corpuscle to bilirubin may occasion- 

 ally take place quite apart from the liver, as shewn by the 

 presence of haematoidin in old blood-clots. 



§ 377. The formation of the bile acids. About this we know 

 still less. Taking glycocholic and taurocholic acids as the typi- 

 cal bile acids, recognizing (§ 207) that these arise from the union 

 of cholalic acid with glycin and taurin respectively, and remem- 

 bering that taurin is found in several tissues, and that glycin 



