282 APPLIED PHYSIOLOGY 



in traces in normal urine, and is often greatly increased 

 in disease. It is identical with the so-called stercobilin 

 of the faeces, and is derived by absorption from the 

 intestine. It is therefore apt to appear in the urine in 

 augmented quantity whenever blood destruction, and 

 therefore bile-pigment formation, is excessive e.g., in 

 extensive extravasations and in pernicious anaemia. 

 Conversely, it disappears from the urine when bile- 

 pigment formation is defective, as in cirrhosis of the 

 liver, or when bile is unable to enter the intestine, as 

 in occlusion of the common duct. 



Excretion by the Liver. 



The liver differs from the kidney as an excretory 

 organ in that it actually forms the waste matters which 

 it excretes, instead of merely picking them out of the 

 blood. This has led to some dispute as to whether 

 bile is to be regarded as an excretion or a secretion, and 

 in the domain of pathology as to whether jaundice may 

 be hsematogenous as well as hepatogenous in origin. 

 Since it has been established by physiologists, however, 

 that the constituents of bile are formed by the liver and 

 do not pre-exist in the blood, it has come to be recognized 

 that all forms of jaundice are in the last resort hepato- 

 genous, or, in other words, that without the liver jaundice 

 would be impossible. 



The chief waste matter which the liver excretes is 

 the pigment derived from the destruction of red blood 

 corpuscles in the portal system. Under the action of 

 the liver cells haemoglobin is converted into haematin, 



