ABSORPTION AND TRANSPORT OF FATS 151 



The subject of phospholipid metabolism has been reviewed by Sin- 

 clair, 718 - 719 while Bloor 720 discussed its role in fat transport. Chaikoff 721 

 considered the application of labeling agents to the study of phospholipid 

 metabolism. 



(c) Partition Theory {Frazer). Although Frazer is rightfully credited 

 with the postulation and development of the so-called "Partition Theory," 

 several earlier workers suggested that the absorption of unhydrolyzed fat 

 occurs when the latter is present in a finely emulsified state. These in- 

 clude Schafer, 688 Heidenhain, 689 Munk, 694 Kitagawa, 722 and Onozaki. 723 

 The details of the Partition Theory were first suggested 724 in 1938; it has 

 recently been reviewed in a comprehensive manner by Frazer. 623 ' 645,725,726 



According to this authority, only part of the ingested fat is hydrolyzed 

 in the intestine; this partially hydrolyzed fraction, consisting of mono- 

 and diglycerides, assists in reducing the bulk of the fat still in the unhydro- 

 lyzed form to a fine emulsion. The neutral fat passes through the intestinal 

 membrane in a finely divided emulsion of negatively charged particles 

 which measure less than 0.5 p. in diameter. Frazer believes that any fatty 

 acids present are absorbed either as soluble compounds or as complexes. 

 More detailed information on the Partition Theory, and a discussion of its 

 relation to the Lipolytic Theory, are given below for the several phases of 

 the digestion process. 



The main points of difference between the lipolytic and the partition 

 hypotheses, insofar as the changes in the lumen are concerned, are sum- 

 marized in Table 17. 



a'. Emulsification : In order that an emulsion system may function in 

 the absorption of fat as such, it must be one in which the particles average 

 less than 0.5 p. It must be produced spontaneously without undue agita- 

 tion, and should be stable for at least three hours. 



One of the most important considerations which influences the ease with 

 which an emulsion is formed, and likewise the stability of the emulsion 

 system, once it is formed, is the pH. Systems which will form a practically 

 permanent emulsion when the medium is alkaline will be immediately re- 



718 R. G. Sinclair, Physiol. Reus., 14, 351-403 (1934). 



719 R. G. Sinclair, Biol. Symposia, 5, 82-98 (1941). 



720 W. R. Bloor, Physiol. Revs., 19, 557-577 (1939). 

 721 1. L. Chaikoff, Physiol. Revs., 22, 291-317 (1942). 



722 R. Kitagawa, Tbhoku J. Exptl. Med., 24, 329-349 (1934). 



723 T. Onozaki, Tbhoku J. Exptl. Med., 29, 224-243 (1936). 



724 A. C. Frazer, Analyst, 63, 308-314 (1938). 



726 A. C. Frazer, Bull. soc. chim. biol, 33, 961-967 (1951). 



726 A. C. Frazer, The Mechanism, of Fat Absorption, in R. T. Williams, Lipid Metabo- 

 lism, Biochem. Soc. Symposia, No. 9, Cambridge Univ. Press, 5-13 (1952). 



