THE ABSORPTION OF THE FOOD-STUFFS 837 



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 amphobolic 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 intestine 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 particles has been actually 

 dissolved out by the digestive juices and has been absorbed in a state 

 of solution. 



We may sum up the processes involved in digestion and absorp- 

 tion of fat as follows. Neutral fat is hydrolysed into fatty acid and 

 glycerin under the action of the gastric juice, the pancreatic juice, 

 and the succus entericus, the effect of the gastric juice being, how- 

 ever, extremely limited unless the fat be presented to it in a finely 

 divided condition. The lipolytic action of the pancreatic juice and 

 succus entericus is largely aided and increased by the simul- 

 taneous presence of bile, which, in virtue of the bile salts lecithin 

 and cholesterin it contains, enables the pancreatic juice to enter 

 into close relation with the fat, and dissolves the products of the 

 activity of the ferment, and so enables it to attack renewed portions 

 of the neutral fat. As the result of this lipolysis there are formed 

 glycerin, which is soluble in water, and fatty acids or soaps, according 

 as the reaction of the medium is acid or alkaline. The alkaline 

 soaps are soluble in water, the soaps of magnesium and calcium are 

 soluble in bile, free fatty acids are soluble in bile acids. The fat 

 is thus reduced to a condition in which it is soluble in the intestinal 

 contents whatever their reaction. In this state of solution its con- 

 stituents are taken up by the cells of the intestinal mucosa. Within 

 the cells a process of synthesis takes place, the soaps being split 

 and the fatty acids thus set free or absorbed, being combined with 

 glycerin with the elimination of water to form neutral fat, which 

 appears as fine granules in the cell protoplasm. By an active process 

 of excretion these granules are extruded in a somewhat more finely 



