836 PHYSIOLOGY 



It is probable that the muscular mechanism of absorption 

 described many years ago by Briicke plays an important part in the 

 absorption of fats, but it is difficult to furnish any experimental 

 proof of the manner in which this mechanism works. Repeated 

 contractions of the muscle fibres of the villus would tend to empty 

 the spaces into the central lacteal, and this in its turn into the sub- 

 mucous plexus of lymphatics, so that the lymph in the spaces is 

 constantly renewed and passes laden with absorbed fat particles 

 into the valved lymphatics of the mesentery. 



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 pancreatic 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 dissolve 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 fa3ces. 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 con- 

 siderably. 



(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, however, 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 



