14 BULLETIN 507, U. S. DEPARTMENT OF AGRICULTURE. 
of a large number of dietary studies, Atwater * found that over 4 per 
cent of the total fat of the diet was furnished by egg yolks. The 
digestibility of this fat is interesting on these grounds alone, but 
when it is considered that egg-yolk fat has associated with it other 
very necessary constituents of the diet, namely, the so-called •''growth- 
maintaining or stimulating factors," which have been the object of 
considerable recent investigation, it becomes of especial interest. 
Osborne and Mendel 2 and McCollum and Davis 3 have studied the 
maintenance and growth-stimulating properties of many fats and have 
found that egg-yolk fat is one of very few which are efficient in this 
respect, and it is also a fat relatively rich in lecithin. 
Although there is little experimental evidence on the subject, it 
is generally said that egg yolks are very quickly and completely 
digested. Observations and experiments on the treatment of the 
underfed led Stern 4 to conclude that egg yolks are well tolerated and 
that they may be used to supply a large proportion of the fat of the 
diet. He found that eggs left the human stomach in from one to 
one and a half hours, and that the coefficient of digestibility of the 
fat (as shown by comparison of the food and feces) was from 96.5 to 
98.5 per cent. 
These results are substantiated by the work of Levites 5 on dogs, in 
which he found that egg-yolk fat was digested in from one to four 
hours. This author concluded that egg-yolk fat behaved differently 
from other fats in the process of digestion, in that the contents 
removed from the stomach of dogs which had been given egg-yolk 
fat showed an alkaline reaction, whereas with olive oil an acid reac- 
tion was obtained. 
According to Lewkowitsch, 6 egg-yolk fat as expressed from the 
yolks of hard-boiled hen eggs is a yellow oil, while that obtained by 
ether extraction is a semisolid oil of an orange-yellow color. For 
the purpose of these experiments, however, it was not considered 
necessary to express or extract the oil, but instead it was fed as it 
occurs in the egg. The yolks were carefully separated from the 
whites, beaten, and incorporated directly in the blancmange, less 
cornstarch being required, owing to the well-known thickening 
properties of egg yolks. The blancmange made with egg yolk had 
a different consistency from that used in previous experiments, being 
more adhesive and pastelike. It also had a characteristic "eggy" 
flavor and furnished about four times as much nitrogen as the blanc- 
mange made with other fats. Five young men, living under normal 
conditions, assisted in the experiments reported on the following page. 
1 Connecticut Storrs Sta. Rpt. 1899, p. 82. 
2 Jour. Biol. Chem., 17 (1914), No. 3, p. 405. 
3 Idem, 15 (1913), No. 1, pp. 107-175. 
* Med. Rec. [N. Y.], 66 (1904), No. 27, pp. 1049-1052. 
^Biochem. Ztschr., 20 (1909), No. 3-5, pp. 220-223. 
6 Chemical Technology and Analysis of Oils, Fats, and Waxes. London: Macmillan & Co., 1909,4. 
ed., vol. 2, p. 395. 
