DIGESTIBILITY OF SOME ANIMAL FATS. 17 
Data of digestion experiments with butter in a simple mixed diet — Continued. 
Weight. 
"Water. 
Protein. 
Fat. 
Carbo- 
hydrates. 
Ash. 
Experiment No. 120, subject E. M : 
Blanc mange containing butter 
Grams. 
2, 198. 
294.0 
1,194.0 
105.0 
Grams. 
1,024.0 
25.0 
1,037.6 
Grams. 
37.2 
39.4 
9.5 
Grams. 
348.8 
3.2 
2.4 
Grams. 
762.5 
221.7 
138.5 
105.0 
Grams. 
25.5 
4.7 
Fruit 
6.0 
Total food consumed 
3,791.0 
84.2 
2,086.6 
86.1 
24.1 
62.0 
354.4 
15.2 
339.2 
1,227.7 
34.8 
1, 192. 9 
36.2 
10.2 
Amount utilized 
26.0 
72.0 
95.7 
97.2 
71.9 
Average food consumed per subject per day. 
1,072.7 
578.7 
29,8 
99.5 
354.4 
10.5 
Summary of digestion experiments with butter in a simple mixed diet. 
Experi- 
ment No. 
Subject. 
Protein. 
Fat. 
Carbo- 
hydrates. 
Ash. 
85 
86 
87 
R. L. S 
I. D.B 
W.D 
Per cent. 
78.3 
63.3 
70.0 
66.3 
66.9 
74.2 
73.3 
72.0 
Per cent. 
93.0 
95.3 
91.2 
96.3 
90.9 
94.7 
93.7 
95.7 
Per cent. 
97.7 
95.6 
95.3 
96.4 
96.5 
96.3 
96.2 
97.2 
Per cent. 
76.0 
67.2 
58.5 
88 
E.M 
71.9 
117 
118 
119 
R.L.S 
I. D.B 
W.D 
51.3 
70.9 
52.1 
120 
E.M 
71.9 
Average 
70.5 
\ 93 -„ 9 
96.4 
65.0 
Having an average digestibility of 93.9 per cent, butter fat may be 
considered more completely assimilated than any of the other animal 
fats considered in this report. Though a reasonable allowance of 
butter is 3 ounces, or 85 grams, per man per day, the experiments as 
a whole emphasize a fact of common experience, namely, that some- 
what larger quantities of butter (100 grams per day at least) may be 
eaten in ordinary circumstances and utilized without any noticeable 
physiological disturbance. 
ALLOWANCE FOR METABOLIC FAT. 
The coefficients of digestibility given in the preceding discussion 
are gross rather than net values. They have been derived in the 
customary way by analyzing the food eaten and the feces excreted 
during an experimental period to determine especially what proportion 
of the ingested fat was available for the maintenance of the needs of 
the body. For this purpose the total ether extract of the feces has 
been taken to represent the actual quantity of undigested fat — the 
unavailable residual of the fat eaten during the experimental period. 
That this assumption is not strictly true is apparent from a study of 
the composition of the feces. It is well known that the feces contain 
not only undigested residues of food, but certain other waste materials, 
