154 



II. DIGESTION AND ABSORPTION OF TATS 



preprandial pattern of blood lipids is reestablished in 4.5 hours. 621 The 

 delay noted for the maximum blood level after a large intake of fat is largely 

 the result of the prolongation of the period during which the food remains 

 in the stomach. Evidence that unhydrolyzed triglycerides, diglycerides, 

 and monoglycerides, rather than glycerol and free fatty acids, are chiefly 

 present four hours after fat is given, is summarized on page 137. 



c'. The Passage of Fat through the Outer Border of the Intestinal Cell: 

 The main points of difference between the Lipolytic and Partition Theories 

 insofar as they refer to the passage of fat through the outer (free) border 

 of the intestinal cell are included in Table 18. 



Table 18 



Comparative Explanations for the Mechanism of the Passage of Fat through 



the Outer Membrane of the Intestinal Cell, as Postulated in the Lipolytic 



and Partition Theories' 1 



Lipolytic theory 



Partition theory 



1. Structure of brush 



border 



2. Fatty acids 



3. Glycerides 



4. Adrenal cortex- 



Solid pavement 



Pass through the mem- 

 brane as soluble com- 

 plexes with bile salts' 



Do not pass through 

 the membrane 



Not concerned here 



Canal structure 6 



Pass through the membrane 

 either as soluble compounds 

 or as complexes 



Pass through the membrane as 

 finely dispersed emulsion of 

 negatively charged particles 

 less than 0.5 m in diameter'' 



Controls normal electrolyte bal- 

 ance, which is closely related 

 to the absorption of charged 

 particles 



a A. C. Frazer, Physiol. Revs., 26, 103-119 (1946). 

 b J. R. Baker, Quart. J. Microscop. Sci., 84, 73-103 (1942). 



c F. Verzar and A. Kuthv, Biochem. Z., 205, 369-379 (1929); 210, 265-280, 281-285 

 (1929); 230, 451-457 (1931). 



d A. C. Frazer, J. H. Schulman, and H. C. Stewart, J. Physiol, 103, 306-316 (1944). 



In developing his theory for the absorption of triglycerides as discrete 

 particles having a diameter under 0.5 u, Frazer 623 first considered the pos- 

 sibility of an anatomical structure suitable for accomplishing this trans- 

 fer. One of the early and frequently repeated statements contrary to the 

 hypothesis of particulate absorption was to the effect that no one had ever 

 observed the histological picture of a globule of fat in the process of passing 

 through the cell membrane. However, this statement cannot be made 

 now without qualification, in view of the fact that Wotton and Zwemer 697 

 have recently reported an observation of this nature. 



By histological examination of the structure of the outside cell membrane, 



