TRANSFERENCE OF FOOD MATERIALS 133 



Hence we conclude that absorption is probably a biological 

 process requiring a transformation of energy.* 



Absorption of Fats. As the fats are the easiest substances 

 to trace their absorption will be described first. We have 

 followed them to the stage of glycerine and fatty acids. The 



FIG. 24. Diagram showing general 

 arrangement of mammalian circu- 

 lation. 



The arrows show the direction of the blood 

 flow. Starting at the right side of the heart 

 (H) the blood goes through the capillaries (C) 

 of the lung (Lg) to the left side of the heart. 

 The arterial blood passes to the capillaries (C) 

 of the head intestine (T), glomerulus of the kid- 

 ney (G), and body generally. 



Before passing back to the heart the blood 

 from the intestine (I) passes through a second 

 set of capillaries (C) of the liver (Lv), to which 

 passes also an arterial blood supply through 

 the Hepatic artery (A) and that from the 

 glomerulus passes through capillaries surround- 

 ing the kidney tubule (T). 



The former double set of capillaries is the 

 portal system and is important in connection 

 with the passage of the product of absorption 

 from the intestine through the liver. The 

 lymphatics (Ly) show the means by which ab- 

 sorbed fats pass from the intestine to the 

 veins at the lower. end of the neck. 



The latter double set of capillaries is impor- 

 tant in connection with the secretion of urine. 

 (Redrawn from Huxley). 



fatty acids are held in solution as soaps and by the bile salts. 

 The contact of the fatty acids with the intestinal wall is 

 promoted by the decrease in surface tension produced by the 

 bile salts. If during digestion of fat the intestine is taken 



* One ought to expect that where a purely physical process is pre- 

 dominant the separating wall shall be thin ; where chemical changes 

 are concerned the cells will be thicker to furnish the protoplasm for 

 the chemical processes. The cells of the intestine are columnar and 

 not squamous, hence we expect to find chemical processes taking place. 



