On the Functions of the Bile as a Solvent. 75 



viz., that gallstones so often consist of almost pure cholestearin. On 

 account of the low solubility of cholestearin, the bile (the excretory 

 agent for this substance) must, even under normal conditions, be almost 

 saturated with it. Hence anything which either diminishes the amount 

 of bile-salts in circulation or increases the amount of cholestearin in the 

 circulation, such, for example, as increased metabolic changes in the 

 nervous tissues, may cause a supersaturation of the bile with cholestearin, 

 and a deposition of that substance. Such a deposition would occur most 

 commonly in the gall bladder where the supersaturated bile is stored 

 for a time, and where absorption of water and probably of bile-salts 

 •also occurs, lowering the solvent power of the contained bile. When 

 precipitation from solution does take place, as is well known under 

 such conditions, the deposition will occur most readily around any 

 nidus of foreign material, such as an epithelial cell. 



In such conditions, it is obviously the supersaturation of the bile 

 with cholestearin which is the primary predisposing factor to gallstone 

 formation, and not the presence of the epithelial cell. When a stone is 

 once started, like a crystal already formed in a solution, its surface is 

 a favourable situation for continued deposit, and so the stone continues 

 to increase in size. The ringed appearance of the cross- section is probably 

 due to alternations in the rapidity of growth, the bile being more satu- 

 rated with cholestearin at some periods than at others. Lecithin and the 

 other constituents of the bile, with the exception of the bile pigments, 

 being very soluble are not represented in the composition of gallstones. 



Conclusions. 



1. Bile has a dual function as a solvent": (a) it acts as a solvent for 

 lecithin and cholestearin, and hence aids in the excretion of those 

 otherwise insoluble bodies by the liver cells, and in their carriage to the 

 intestine ; (b) it acts as a solvent in the intestine for both free fatty acids 

 and soaps, conferring their entire solubility on the former, and largely 

 increasing the solubility of the latter. 



2. These solvent properties of the bile are chiefly due to the bile 

 salts ; but in the case of the fatty acids and soaps the amount dissolved 

 is greatly increased by the simultaneous presence of lecithin. 



3. These solvent actions of the bile salts explain the utility of the 

 reabsorption of the bile-salts and their circulation through the liver, so 

 that they may be used over and over again as solvent agents. In absorp- 

 tion, the bile salts carry the soaps of fatty acids into the columnar cells ; 

 in the liver, they are absorbed by the liver cells, carry the excretory 

 lecithin and cholestearin with them, and are passed into the bile canali- 

 culi holding these substances in solution ; in the bile, the lecithin and 

 cholestearin are carried in solution to the intestine; and in the in- 

 testine, the soaps and fatty acids are dissolved and rendered capable of 



