OUTPUT OF WASTE MATTER 141 



acid, cholalic acid, associated with glycin in 

 glycocholic and with taurin in taurocholie 

 acid. Both the origin and the ultimate fate 

 of the bile salts are in obscurity. As they both 

 contain nitrogen, and one contains sulphur, 

 we must look for their origin in protein 

 metabolism, but we know nothing of the steps 

 of the process. In the bile (in human bile 

 glycocholate of soda forms the chief part of 

 the solids) they reach the intestine. We are 

 not aware of any special function fulfilled by 

 them in connection with either intestinal 

 digestion or intestinal absorption. Only a 

 very small amount of the bile salts appears 

 in the faeces. It follows that they must be 

 re-absorbed and carried back to the liver by 

 the portal circulation and again eliminated 

 in the bile. Thus a kind of bile-salt circula- 

 tion has been imagined, but there is no hint 

 as to any use of this arrangement. Traces 

 of substances may appear in the urine that 

 may have originated from chemical changes 

 in the bile salts. Lastly, small quantities of 

 cholesterin or cholesterol may be found in bile. 

 It forms the chief constituent of gall-stones, 



