2 BULLETIN 507, U. S. DEPAETMENT OF AGRICULTURE. 
by the work of Tangl and Erdelyi 1 and of Yon Fejer, 2 who have 
observed that fats with a melting point somewhat higher than 
normal body temperature do not leave the stomach so readily as 
those of a lower melting point, and, furthermore, 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 3 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 4 and Osborne and Mendel, 5 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, 6 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 7 
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 
J Biochem. Ztschr., 34 (1911), No. 1-2, pp. 94-110. 
2 Idem, 53 (1913), No. 1-2, pp. 168-178. 
s Jour. Biol. Chem., 22 (1915), No. 1, pp. 15-41; Cornell Univ. Med. Bui., 5 (1915), No. 2 (pU 1, paper 14). 
< Jour. Biol. Chem., 15 (1913), No. 1, pp. 107-175. 
5 Idem, 16 (1913), No. 3, pp. 423-437; 17 (1914), No. 3, pp. 401-408. 
e Idem, 17 (1914), No. 2, pp. 107-119. 
i U. S. Dept. Agr., Office Expt. Stas. Bui. 143 (1904), pp. 57-77. 
