14 BULLETIN 507^ U. S. DEPARTMENT OF AGEICULTURE. 



of a large nimiber 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 stimulatmg factors," which have been the object of 

 considerable recent investigation, it becomes of especial interest. 

 Osborne and Mendel ^ and McCoUum and Davis ^ 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 Uttle 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 * to conclude that egg yolks are weU 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^ 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,® 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, 



' Connecticut Storrs Sta. Rpt. 1899, p. 82. 

 2 Jour. Biol. Chem., 17 (1914), No. 3, p. 405. 

 a Idem, 1.5 (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. 



'Chemical Technology and Analysis of Oils, Fats, and Waxes. London: Macmillan & Co., 1909,4. 

 ed., vol. 2, p. 395. 



