140 PRINCIPLES OF PHYSIOLOGY 



of the pigments of the urine. The origin of 

 these pigments is undoubtedly the decom- 

 position of the haemoglobin of effete or 

 worn out red blood corpuscles. Where the 

 haemoglobin is set free and decomposed is 

 doubtful. This probably occurs both in the 

 spleen and in the liver. It is important to 

 note that all the blood that has passed through 

 the spleen goes to the liver. The relation of 

 bilirubin to the blood pigment is undoubted, 

 as haemoglobin is a compound of haema- 

 tin, containing the all-important iron, and a 

 globulin. If the iron is removed from haematin 

 we have a body called haematoidin, or iron-free 

 haematin, produced. This is identical with 

 bilirubin. Thus we see the steps of the pro- 

 cess for the elimination of waste pigmentary 

 matters 



74. The bile contains the sodium salts of 

 highly complicated acids, known as the 

 bile acids, forming glycocholate and tauro- 

 cholate of sodium. The first is the more 

 abundant in human bile. Both contain 

 nitrogen ; taurocholic acid alone contains 

 sulphur. Each may be split up into (a) an 



