ABSORPTION AND TRANSPORT OF FATS 155 



referred to as the "brush-border," Baker 732 detected the presence of a sys- 

 tem of fine canals, running at right angles to the surface, which might allow 

 particles having a diameter of less than 0.5 w to pass. These canals were 

 visible when the tissues were examined in transverse or longitudinal sec- 

 tions. Although Baker's observations were made on the intestine of am- 

 phibia, they do offer a suggestion as to the possibility of an anatomical 

 basis for the Partition Theory in the higher animals. 



One should be able to prove that, if this canalicular structure is able to 

 function, materials can be absorbed when present in a sufficiently fine 

 emulsion, whereas they are not absorbable when present in unemulsified 

 or coarsely emulsified form. The best substance on which to test this 

 hypothesis is paraffin. There are contradictory statements in the litera- 

 ture as to whether or not paraffin is absorbed (see Chap. IV), inasmuch 

 as these earlier experiments were not controlled as regards the size of the 

 emulsion particles. The only way to answer the question satisfactorily is to 

 introduce an emulsion of known size directly into the small intestine, since 

 passage of an emulsion through the stomach may largely alter the size of its 

 particles. Frazer, Schulman, and Stewart 729 demonstrated that, when 

 paraffin emulsions having an average particle diameter of less than 0.5 n 

 were introduced ( intraduodenally into rats, absorption was comparable 

 with that existing when a similar olive oil emulsion was given. This phe- 

 nomenon was repeatedly confirmed by these workers, and by Frazer alone, 733 

 using large numbers of rats, by the use of histological examination and resid- 

 ual analyses. Bernhard and Scheitlin 734 supplied additional evidence of 

 particulate absorption by demonstrating that finely emulsified mineral oil 

 is taken up by the intestinal mucosa. Moreover, Bernhard et al. 735 reported 

 further confirmation of particulate absorption by the finding that a series 

 of hydrocarbons from C 8 to Ci 8 , labeled with deuterium in the 1,2 or 2,3 

 position, were absorbed and metabolized. 



The mechanism of absorption of fats through the intestinal wall has 

 been shown to have an analogy with the passage of fat through the cell 

 membrane of the soybean. Heupke and Rost 736 demonstrated that duo- 

 denal juice is able to liberate the fat from the plant cells; it could be dis- 

 solved under these conditions by human or ox bile at a pH of 6.5. Bile salts 

 and fatty acids were present in a 1:1 ratio. This dissolved fat readily 

 passed through the cell wall in either direction. 



732 J. R. Baker, Quart. J. Microscop. Sci., 84, Part I, 73-103 (1942). 



733 A. C. Frazer, Biochem. J., 51, xiii (1952). 



734 K. Bernhard and E. Scheitlin, Helv. Physiol, et Pharmacol. Acta, 10, 54-61 (1952). 

 736 K. Bernhard, U. Gloor, and E. Scheitlin, Helv. Chim. Acta, 35, 1908-1913 (1952). 

 736 W. Heupke and G. Rost, Z. physiol. Chem., 284, 204-210 (1949). 



