164 II. DIGESTION AND ABSORPTION OF FATS 



(S) The Transfer of Fat to the Interior of the Villi 



a. Introduction. Less information is available as to the mechanism by 

 which fat passes from the epithelial cells to the interior of the villi than is 

 known concerning its passage into these cells. Fat accumulates in the in- 

 testinal cells during fat absorption, but a continual stream of this food- 

 stuff must pass into the chyle, and thence into the circulation, during the 

 entire period of fat absorption ; the lipemia occurring for the period of four 

 to six hours after fat has been ingested can only be a reflection of the fat 

 which has passed the barriers of the intestinal cells and gained access to the 

 lymph and blood stream. Several theories have been proposed to account 

 for the transfer of the fat particles from the cell to the interior of the villus. 



b. Theories for the Mechanism of Transfer, (a) Theory of Schdfer. m 

 This hypothesis recognizes that the leucocytes play an important role in the 

 transport of fat. According to Schafer's observations, the leucocytes in the 

 intestinal wall are always full of fat, irrespective of whether little or much 

 fat is being absorbed. It was considered that the function of the intestinal 

 cells is to receive the hydrolysis products of fat, to synthesize them into 

 triglycerides, and to store them until the leucocytes can transport them into 

 the lacteals. The experiments of Clark and Clark 690 are interpreted as 

 offering support to the Schafer hypothesis. In these tests, it was shown 

 that leucocytes were instrumental in removing fat injected into the muscu- 

 lature of the tail of the tadpole. When drops of fat 30 to 70 n in diameter 

 were introduced, leucocytes were observed to pass through the walls of the 

 blood vessels and to wander in the direction of the fat droplets. On reach- 

 ing one of these, the leucocyte flattened out and formed a ring around the 

 globule, becoming pigmented as it engulfed it. The lymph vessels gradually 

 extended out to the oil and remained in contact with the leucocytes and the 

 oil until the latter was dissipated. 



In the case of fat transport in the intestine, it has been suggested that the 

 leucocytes engulf the small fat particles either in the epithelial cells or after 

 they have been extruded through the basement membrane of the intestinal 

 cells; these leucocytes then carry the fat droplets through the intercellular 

 spaces within the villus to the lacteal. When the leucocytes pass inside these 

 lacteals, they disgorge the fat, which then passes into the lymphatic chan- 

 nels. Presumably, a somewhat similar mechanism may explain the passage 

 of the fat into the capillaries. 



(b) Theory of Heidenhain}* 9 Heidenhain agrees with Schafer that the 

 fat from the epithelial cells is transferred to the lacteals without alteration, 

 except in the size of the particles. However, this latter investigator be- 

 lieved that the contraction of the protoplasm was responsible for the trans- 



