742 PHYSIOLOGY 



It was long considered that the fats were taken up by the epithelial cells 

 from the intestine as fine particles of neutral fat, the chief use of the pan- 

 creatic juice being to aid the formation of an emulsion of fat in the intestines. 

 There seems to be little doubt that this was an error, and that the fats are 

 absorbed, dissolved in the bile, either as soap or as fatty acid. The arguments 

 for this view can be shortly summarised as follows ; 



(1) Although the bile does not dissolve neutral fats, it has a strong solvent 

 action on fatty acids, on soaps, and even on the insoluble calcium soaps. 

 This solvent power is greatest in the case of oleic acid, of which bile can dis- 

 solve 19 per cent. It is very small in the case of pure stearic acid, but the 

 solubility of the latter acid is largely increased if it be associated as usual with 

 oleic acid. Moore has shown that this solvent action is chiefly conditioned 

 by the bile salts, aided by the lecithin and cholesterin also present in the bile, 

 a solution of lecithin and cholesterin in bile salts having a greater solvent 

 power than the salts alone. 



(2) The presence of bile in the intestine is essential for the normal 

 absorption of fat. If the bile be cut off by occlusion of the bile ducts or by 

 the establishment of a biliary fistula, the utilisation of fat sinks from about 

 98 per cent, to about 40 per cent., the unabsorbed fat appearing in the 

 faeces. This large undigested residue of fat hinders also the absorption of 

 the other food-stuffs by covering them with an insoluble layer, so that 

 nutrition as a whole may suffer considerably. 



(3) Absorption may also be interfered with by ligature of the pancreatic 

 duct. This result is probably due to the absence of the fat-splitting ferments 

 of the pancreatic juice from the intestine. If the faeces be analysed it is found 

 that a very large proportion of the fat has been split into fatty acids in the 

 course of its passage through the alimentary canal. This lipolysis has, how- 

 ever, been carried out by the agency of micro-organisms, i.e. in the lower 

 segments of the gut where the greater part of the bile has been already re- 

 absorbed into the portal circulation. If fat be given to animals deprived 

 of their pancreas, in a finely divided form, such as cream or milk, a certain 

 proportion of it is absorbed. Under these conditions a considerable degree 

 of lipolysis may occur in the stomach itself, so that the fats would be already 

 hydrolysed when they came in contact with the bile in the duodenum. 



(4) It was shown by Schiff, by means of his amphibolic fistula, that the 

 bile which is poured into the gut undergoes a circulation, being re- absorbed 

 from the lower parts of the digestive tube, carried to the liver by the portal 

 vein, and re-secreted in the bile. The same quantity of bile salts may 

 therefore be used over and over again as a vehicle for the transfer of the fatty 

 acid and soaps from the lumen of the gut into the epithelial cells. 



(5) Substances which are physically almost identical with fats, e.g. 

 petroleum or paraffin, are not absorbed even when introduced into the intes- 

 tine in the finest possible emulsion. If neutral fat be melted with a soft 

 paraffin and the resulting mixture made into a fine emulsion and administered 

 it is found that the intestine rejects the paraffin, but takes up the neutral 

 fat. This result can only be explained by assuming that the fat in the 



