CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 747 



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 suggested that the red marrow of bim<^ 

 is one of these ; but further information on these points is needed. 



Assuming that under normal circumstances the chief supply of 

 material for the manufacture of bilirubin comes from the spleen, 

 the question arises, Does that material leave the spleen in the form 

 of haemoglobin, or does the spleen still further assist in the matter, 

 by effecting some preliminary change in the haemoglobin, by 

 converting it for instance into a proteid-less ha?matin-like body ? 

 And the same question may be also applied to the other tissues 

 which may similarly provide material. Our knowledge is at 

 present insufficient to furnish a satisfactory answer to such a 

 question. 



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 beyond this is at present uncertain. 

 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 occasionally 

 take place quite apart from the liver, as shewn by the presence of 

 hgematoidin in old blood-clots. 



479. The formation of the bile-acids. About this we know 

 still less. Taking glycocholic and taurocholic acids as the typical 

 bile acids, recognizing ( 246) that these arise from the union 

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

 membering that taurin is found in several tissues, and that 

 glycin (see 419) though not an actual constituent of any of 

 the tissues must certainly arise in tissue metabolism^ we may 

 conclude that the chief work in this respect of the hepatic 

 cell is to provide the cholalic acid, and to effect the combination 

 with glycin and taurin, though possibly some amount of either 

 one or the other of these bodies may be furnished by the 

 hepatic substance itself. As to how cholalic acid arises out of 

 the metabolism of the hepatic cell we know no more than we 

 do about the formation of kreatin in muscle or of pepsin in a 

 gastric cell. We are equally ignorant about the origin of glycin 

 and taurin, and cannot explain why in one animal glycocholic, 

 and in another taurocholic acid is prominent in the bile, though 

 the two bodies, as shewn especially by the presence of sulphur 

 in the taurin, are widely different. It has been observed 

 that the presence of bile in the intestine seems to excite the 

 liver to increased biliary action ; since the bile-acids are rapidly 

 changed in the intestine and the cholalic acid speedily altered, it 

 seems probable that the increased biliary activity is due to the 



