EXCRETION OF LIPIDS BY WAY OF LARGE INTESTINE 345 



It was early demonstrated that, under ordinary dietary conditions, 

 fecal fat has a different composition from that of ingested fat, and that 

 the quantity excreted bears little relation to that of the ingested fat. Hill 

 and Bloor 616 showed that fat was invariably present in the feces, irrespec- 

 tive of whether or not this foodstuff was included in the diet. When 

 moderate amounts of fat were present in the diet, no appreciable increase 

 in fecal fat resulted. 615 - 616 Hill and Bloor 616 concluded that fecal fat is not 

 unabsorbed food fat, but is rather in the nature of an excretion, either 

 directly from the blood or indirectly from intestinal secretions. Holmes 

 and Kerr 617 compared the iodine numbers and saponification values of 

 food fats and fecal fats of human subjects who had ingested the several 

 fatty substances. The values for the iodine number of the food and of 

 fecal fats are respectively as follows: goose fat tests, 68.5 and 28.6; oleo 

 oil tests, 44.3 and 27.9; and corn oil tests, 123.1 and 34.3. The compara- 

 tive results on saponification values were as follows: goose fat tests, 

 194.8 and 159.1; oleo oil tests, 207.3 and 146.2; corn oil tests (no value 

 reported for oil fed, but average saponification value is 190), 108.6 (fecal 

 fat). 



On the basis of an. extensive study, using cats and dogs, Sperry and 

 Bloor 618 concluded that fecal fats do not originate from food fat because: 

 (1) there is almost as much fecal fat on a fat-free diet as on a fat-rich 

 regimen, (2) during fasting there is considerable excretion of lipids with 

 properties resembling those of the lipid excreted when fat is given, and 

 (3) the composition of food fat differs from that of fecal fat. However, 

 ingested fat does to some extent influence fecal fat, since somewhat higher 

 fecal lipids do occur on a fat diet than on a fat-free regimen, and the com- 

 position of solid and of liquid fatty acids in the feces bears some relation- 

 ship to these fractions in the food fats. 



Another distinguishing factor which indicates the difference which 

 exists between food fat and fecal fat is the melting point. Fecal fat usually 

 has an appreciably higher melting point than does the corresponding food 

 fat. Thus, the values for food and for fecal fat in the dog were 43° and 

 50.5°C, respectively, after the feeding of lard, and 52 and 56.0°C. after 

 mutton fat was given. 619 In man, the feces fat melted at 50 to 51.5°C. 

 after milk fat (43 °C.) was fed 619 ; after the ingestion of lard (35 to 37 °C), 



615 E. Hill and W. R. Bloor, /. Biol. Chem., 53, 171-178 (1922). 



616 A. Krakower, Am. J. Physiol, 107, 49-54 (1934). 



617 A. D. Holmes and R. H. Kerr, J. Biol. Chem., 58, 377-381 (1923). 



618 W. M. Sperry and W. R. Bloor, /. Biol. Chem., 60, 261-287 (1924). 



619 F. Muller, Z. klin. Med., 12, 45-113 (1887). 



