ii EXTERNAL DIGESTIVE SECRETIONS 143 



of the two pressures, measured simultaneously by Heideuhain on 

 dogs. This phenomenon, perfectly analogous with that which 

 Ludwig found for the salivary secretion, shows that the bile 

 secretion cannot, even if it fluctuates with the variations in the 

 circulatory conditions of the liver, be regarded as an effect of 

 simple filtration through the vessel walls, but must depend on the 

 activity of the hepatic secretory cells. 



In proportion as the elimination of bile by the excretory duct 

 is obstructed, it is reabsorbed, and the phenomena of jaundice 

 appear. The skin and conjunctiva of the eye become yellow, 

 which is the external sign of cholaemia, or admixture of bile with 

 blood. The bile is not absorbed directly by the blood-vessels of 

 the liver, but by the lymphatics, which convey it to the thoracic 

 duct, whence it is poured out into the blood torrent. This fact, 

 already surmised by Sanders in 1795, was demonstrated experi- 

 mentally by von Fleischl in 1872. Harley has recently shown 

 that if after ligation of the choledochus the thoracic duct is also 

 tied in a dog, there will for 17 days be no constituents of bile, 

 either in the blood or the urine, and no external sign of jaundice. 

 In this case, all the bile collects in the gall-bladder, and along the 

 thoracic duct and its roots in the liver. 



XXI. The bile collected from the gall-bladder of dead bodies, 

 or obtained by fistula from man and other animals, is a mixture 

 of the secretion from the hepatic cells, and that of the epithelia 

 which line the bile ducts and gall-bladder. Along the excretory 

 ducts, the products of the hepatic cells are mingled with mucus 

 and cells in process of disintegration, which make it more dense, 

 more viscid, and less limpid and transparent. The reaction is 

 alkaline from the carbonate and phosphate of sodium, the colour 

 varies in different animals (golden-yellow in carnivora, grass-green 

 in herbivora, greenish-yellow in man), the taste is bitter. That 

 of man, exclusive of mucus, contains O'5-l per cent solids, of 

 which 0'7-0'8 per cent are mineral. Within the gall-bladder it 

 condenses from absorption of water ^till the solids amount to 

 16-17 per cent with specific gravity 1-010-1-040. 



The specific constituents of bile are the Hie acids and 

 pigments. 



The Hie acids are never found in the free state, but always in 

 the form of sodium salts (potassium salts in sea fishes). They are 

 acids containing nitrogen, and are composed of cholalic acid (or 

 related acids), glycine and taurine. It is remarkable that the 

 quantity of cholalic acid never varies sensibly in animals of the 

 same species. On the other hand, in different biles the relative 

 amount of glycocholic and taurocholic acid may vary, although 

 the former always exceeds the latter in quantity. Besides 

 cholalic acid, according to Schotten and Lassar Cohn, human bile 

 contains two other related acids fellinic and choleinic acid, which 



