74 



Messrs. B, Moore and W. H. Parker. 



4. Lecithin. — The power which aqueous solutions of bile-salts 

 possess of taking up a large quantity of lecithin into clear solution at 

 body temperature is very interesting from the point of view of the re- 

 absorption of the bile-salts, as is also the fact that in presence of 

 lecithin the solvent power is greatly increased for other fatty sub- 

 stances, such as the free fatty acids and soaps, as is shown by the fore- 

 going figures. 



Pure lecithin is practically insoluble in water, the addition of as- 

 little as Ol per cent, causes an opalescence, and further additions give 

 rise, as is well known, to a kind of emulsion. But when lecithin is 

 added to a 5 per cent, solution of bile-salts,* the appearances observed 

 are quite different. 



The lecithin dissolves to a clear brown-coloured solution, and the 

 amount taken up is surprising ; thus a 5 per cent, solution takes up no 

 less than 7 per cent, of lecithin at a temperature of 37° G. On cool- 

 ing, part of the lecithin is thrown out of solution as a finely suspended 

 precipitate or emulsion, which glistens with a silky lustre when the 

 test-tube containing it is shaken so as to set the fluid in motion. At 

 ordinary room temperatures of 15° to 20° C, a considerable amount of 

 lecithin, 4 to 5 per cent., is, however, still retained in solution. 



The power of lecithin in increasing the solubilities of the fatty acids 

 and soaps, explains in great part why lower solubilities are obtained in 

 experimenting with pure bile-salt solutions, than with bile. The 

 lecithin naturally occurring in bile thus increases the solvent power of 

 that fluid in the intestine for fatty acids and soaps. 



5. Cholestearin. — After the high solubility obtained for lecithin, 

 we were much surprised at the excessively low solubility obtained for 

 cholestearin, and proceeded as above described to make preparations of 

 pure cholestearin from several different sources. The experimental 

 results obtained were however uniform ; in all cases it was found that 

 while cholestearin is appreciably more soluble in bile-salt solutions than 

 in water, in which it appears to be absolutely insoluble, yet the degree 

 of solubility is very low. Thus, in several experiments with ox bile, we 

 were unable to dissolve O'l per cent, of cholestearin additional, and as 

 far as we could judge most samples of bile are practically saturated 

 with cholestearin. A 5 per cent, solution of bile-salts dissolves about 

 0*1 per cent, of cholestearin, and the amount is not very appreciably 

 increased by the simultaneous presence of lecithin ; at any rate, the 

 amount dissolved by 5 per cent, of bile-salts plus 1 per cent, of lecithin 

 does not exceed 0*15 per cent. 



This exceedingly low solubility of cholestearin in bile furnishes an 

 interesting experimental explanation of a well-known clinical fact, 



* The same results are obtained when lecithin is added to bile ; thus a sample 

 of ox bile dissolved 6 per cent, at 36° C. This shows that bile is not nearly 

 saturated with lecithin under normal conditions of its secretion. 



