EXCRETION 283 



then into haemochromogen, and finally into bilirubin, 

 which is the cause of the golden-yellow colour of normal 

 fresh bile. If the destruction of blood corpuscles be 

 excessive, so much bile pigment may be formed that the 

 bile capillaries get choked, and some of the bile is re- 

 absorbed hence the so-called 'haematogenous' jaundice; 

 whilst, if the destruction be greater still, some haemo- 

 globin may escape into the bile unconverted, or even 

 into the general circulation, and reach the urine. 



In the intestine bilirubin is reduced under the action 

 of micro-organisms to urobilin ; but if diarrhoea be present 

 there is no time for this to take place, and the stools 

 may then contain bile pigment. Owing to the absence 

 of micro-organisms from the intestine of the newly-born 

 child, the meconium contains no urobilin. 



Bile pigment seems to act like a weak acid, and forms 

 salts with alkalies or earth : a combination of bilirubin 

 with calcium, for instance, is a common ingredient of 

 gall-stones. 



The ultimate source of the bile acids is unknown, but 

 they may fairly be regarded as excretory products, for 

 from 30 to 40 per cent, of them appears in the fasces, 

 and traces also in the urine. The remaining 50 to 

 60 per cent., however, is reabsorbed from the intestine, 

 and returned to the liver, to be again excreted. This 

 circulation of the larger part of the bile acids between 

 the intestine and liver is rather peculiar, and it is diffi- 

 cult to see the reason for it. It is true that the bile 

 salts incidentally aid in keeping the cholesterin of the 

 bile in solution, and by this circulatory arrangement 

 a small amount of bile salts is enabled to go a long way, 



