LIPID CONTENT AND COMPOSITION OF ANIMAL 557 



in Marseilles. 180,181 It has been used for the investigation of body composi- 

 tion by Reynolds 182 at the Fels Research Institute for the Study of Human 

 Development, at Antioch College. In order to obtain consistent results, it 

 was necessary to take the roentgenograms at precise locations. In the 

 trochanteric region, relatively slight changes in the level at which the 

 width of the fat layer was measured caused variations of as much as 50% in 

 the values obtained. 



d'. Direct Measurement of The Thickness of the Subcutaneous Layer: 

 Another procedure, employed mainly in the case of hogs, by McKeekan, 183 

 involves the determination of the thickness of the fat layer along the back 

 line. Hazel and Kline 184 employed this method by first making small skin 

 incisions into the back at certain points, and then measuring the depth to 

 which a narrow metal ruler could be inserted before it was stopped by a 

 well-defined muscle layer. 



(c) The Use of Density Measurements. Since the density of body fat is 

 considerably less than that of the fat-free constituents of the tissues, the 

 figure for the density of the body as a whole will vary according to the rel- 

 ative proportion of fat. The higher the content of fat of the body, the 

 lower will be the value recorded for its density. The density of the entire 

 body is simply the weight divided by the volume which it occupies. The 

 latter value can be readily obtained by determining the weight of the ob- 

 ject completely submerged in water as compared with that when it is sur- 

 rounded by air. Keys and Brozek 166 presented the following formula for 

 the estimation of specific gravity : 



<a n OT - Ma 



ap - & - M A -Ml- DwVr 



where M A is the weight in air, M' w is apparent weight under water, D w is 

 density of water in tank, and V R is weight of water displaced by residual 

 air (lungs and respiratory passages) . 



According to Keys and Brozek, m the specific gravity of the fat-free evis- 

 cerated body of the guinea pig was estimated by Pace and Rathbun 185 at 

 1.0939; Keys and Brozek calculated it as 1.0934. In the case of man, 

 Rathbun and Pace 186 cited a value of 1.10 for the density of the fat-free 



180 H. C. Stuart and D. KuhJman, J. Pediat., 20, 424-453 (1942). 



181 H. C. Stuart, J. Pediat., 25, 257-264 (1944). 



182 E. L. Reynolds, Distribution of Subcutaneous Fat in Childhood and Adolescence. 

 Monogr. Soc. Research Child Develop., 15, Ser. 50, No. 2, 1950. Child Develop. Publ., 

 Evanston, 111., 1951. 



183 C. P. McKeekan, J. Agr. Sci. (England), SI, Part I, 1-49 (1941). 



184 L. N. Hazel and E. A. Kline, J. Animal Sci., 11, 313-318 (1952). 

 186 N. Pace and E. N. Rathbun, J. Biol. Chem., 158, 685-691 (1945). 

 186 E. N. Rathbun and N. Pace, J. Biol. Chem., 158, 667-676 (1945). 



