70 



On the Funct ions of the Bile as a Solvent. 



being taken in along with the bile-salts by the columnar cells, while 

 the lecithin and cholestearin which are incapable of absorption are 

 precipitated as the bile-salts are absorbed. 



4. Lecithin possesses a high solubility in the bile, and cholestearin a 

 very low solubility. The low solubility of cholestearin furnishes an 

 explanation of the fact that gallstones are composed almost entirely 

 of this substance. 



5. The sodium soaps possess only a low solubility in water, the palmi- 

 tate and stearate being practically insoluble ; but the solubility is 

 increased by the presence of bile-salts, and especially in the presence 

 of lecithin ; further, the character of the solution is different in the two 

 cases, being less colloidal when in bile-salt solution. 



6. Even in bile or bile-salt solution the calcium and magnesium soaps 

 have a low solubility, but of the two the magnesium soaps are the more 

 soluble. 



7. These results cast some light on the relative functions of the pan- 

 creatic juice and bile in fat digestion and absorption. The enzyme of 

 the pancreatic juice splits up the neutral fats, forming free fatty acids, 

 which are largely converted into soaps by the alkali present ; while the 

 bile gives solubility to the fatty acids and soaps so produced. Now it 

 is well known that the fat-absorbing power is impaired but not com- 

 pletely destroyed by the absence of either one secretion, but is 

 practically lost when both secretions are absent. These facts can 

 probably be best explained as follows : — (a) In the absence of the 

 pancreatic ferment, since the bile has no action upon neutral 

 fats, and these are insoluble, only that portion can be absorbed 

 which is free in the fat when ingested, or is set free in the stomach, 

 or by bacterial action in the intestine. Since bacterial action is at 

 a minimum in the small intestine, the fat in great part is not set 

 free until the large intestine is reached, when the bile salts have all 

 been reabsorbed, and hence cannot assist in solution. Accordingly, in 

 the absence of the pancreatic secretion, a large percentage of the fat 

 appears as fatty acids in the fasces, (b) In the absence of the bile, 

 although the fat is decomposed high up in the intestine and converted 

 into fatty acids and soaps, the absorption is slow because the solvent 

 action of the bile is wanting, and hence only a fraction is absorbed, and 

 the remainder passes on chiefly as fatty acid to be thrown out in the 

 fasces. When both pancreatic secretion and bile are absent, in the 

 first place only a small amount is decomposed in the small intestine, 

 and in the second place there is nothing to confer solubility on this 

 small portion, with the result that absorption falls almost to zero. 



