2 BULLETIN 507, U. S. DEPARTMENT OF AGEICULTUEE. 



by the work of Tangl and Erdelyi^ and of Von Fejer,- who have 

 observed that fats with a melting point somewhat higher than 

 normal body temperatm'e do not leave the stomach so readily as 

 those of a lower melting point, and, fm^thermore, that they are not 

 so easily emulsified in the intestine. Apparently no connection has 

 been shown between these observations and thoroughness of diges- 

 tion. Before one can assume that the fuel value of fat, or more 

 accurately the fuel value of digested fat, actually represents its 

 energy value to the body, one must take into account such work as 

 that of Lusk-^ and his associates, which showed that the digestion 

 and assimilation of foods (including fat) caused an increased output 

 of energy, not ascribable to muscular work, and designated specific- 

 dynamic effect. The test reported did not compare different fats. 



That in comparing fats we must consider not alone such questions 

 of thoroughness of digestion and energy expenditure as a result of 

 digestion and their relation to nutrition is apparent from recent work 

 of McCollum and Davis ^ and Osborne and Mendel,^ who concluded 

 that certain fats carry either as an integral part or as a complement 

 a small amount of substance important in growth. In discussing 

 dietetics, it is commonly assumed that fat and carbohydrates can 

 replace each other as sources of energy in proportion to their theo- 

 retical energy values. There are times when it is not wise to do 

 this, at least under pathological conditions, as recent work would 

 indicate, since, according to Ringer,® there is a limit beyond which 

 this replacement can not go without serious results, some carbohy- 

 drate, it is claimed, being essential for the complete combustion of fat. 



EXPERIMENTAL METHODS. 



The investigations here reported form a part of a series of studies 

 of the thoroughness of digestion of culinary and table fats of animal 

 and vegetable origin, including those eaten as such, those added to 

 foods in cookery, and those which form an integral part of the foods 

 in which they naturally occur. In all the same general procedure 

 was followed. 



The experimental methods were those adopted in earlier work ^ 

 carried on by the department as a part of its investigations of the 

 nutritive value of foods as a result of extended studies of the advan- 

 tages and disadvantages of differences in technique and in laboratory 

 methods. 



The subjects were young men (medical or dental students) in 

 good health, of similar occupation and muscular activity. The diets 



1 Biochem. Ztsfhr., 34 (1911), No. 1-2, pp. 94-110. 



2 Idem, 53 (1913;, No. 1-2, pp. 1G8-178. 



3 Jour. Biol. Chem., 22 (191.5), No. 1, pp. 1;5-41; Cornell Univ. Med. Bill., 5 (1915), No. 2 (pU 1, paper 14). 

 * Jour. Biol. Chem., 15 (1913), No. 1, pp. 167-175. 



6 Idem, 16 (1913), No. 3, pp. 423-437; 17 (1914), No. 3, pp. 401-408. 



« Idem, 17 (1914), No. 2, pp. 107-119. 



' U. S. Dept. Agr., Office Expt. Stas. Bui. 143 (1904), pp. .57-77. 



