200 W. E. BLOOR 



amount absorbed and second by mixing it with enough low melting fat to 

 bring tbe melting point of the mixture to somewhere near body tempera- 

 ture. (.Recent work by Lyinan indicates that available glycerol may be a 

 limiting factor in absorption of the simple esters, just as it is with the 

 fatty acids.) 



Aside from the high melting fats and excepting certain ones like 

 castor oil which are either irritating to the intestine or which form irritat- 

 ing soaps, there appears to be little difference in the extent of utilization 

 of fats of whatever origin, animal or vegetable, a result which might have 

 been foretold since the fatty acids in combination in fats from various 

 sources are largely the same, the main difference being in the relative 

 amounts of each constituent of the mixture. 



Emulsified lion in Fat Digestion and Absorption. It is generally 

 assumed that fats must be emulsified in the intestine before they can be 

 digested and absorbed, for the reason that while the lipases found in the 

 intestinal secretions are always in water solution the fats are insoluble 

 in water and lipolysis can take place only at the surface, which emulsifica- 

 tion greatly increases. The assumption has the support of a large number 

 of observations on fat in the intestine during digestion. That emulsions 

 are not always present in the intestine under these conditions is, however, 

 attested by observations of Moore and Rockwood, who found in many cases 

 no emulsion but a brownish liquid with an acid reaction. No examination 

 was made as to whether this liquid contained fat and it is possible that it 

 consisted of a bile solution of the fatty acids. Where conditions for diges- 

 tion are exceptionally good the emulsion may be only transitory. The 

 conditions for the emulsification of the food fat on its entry into the in- 

 testine are ordinarily very favorable. There are present free fatty acid 

 in the fat, alkali in the secretions, and other substances such as proteins, 

 lecithin, etc., which are either emulsifiers themselves or which act to 

 stabilize emulsions. The acidity of the intestine which many observers 

 have found need not be a hindrance since it is due mainly to carbonic acid 

 and emulsions formed with the aid of pancreatic secretion and bile are 

 known to be stable in solutions of carbonic acid. 



Summary. It will be seen that no definite answer can yet be given 

 as to the way in which fat passes through the intestinal wall. 

 Emulsification is probably at least an early if temporary step. Hydrolysis 

 undoubtedly takes place in large measure and would therefore seem 

 to be a necessary preliminary to absorption. Soap formation under the 

 conditions of reactions of the intestinal contents (faint acidity) and 

 the presence of bile probably takes place to a considerable extent. Soap 

 being water-soluble is assumed by many to be the form in which the fats 

 are finally absorbed, but it should be borne in mind first that soap 

 is a difficultly diffusible substance and second that in water solution 

 it hydrolyzes, forming aggregates of free fatty acid which would be still 



