LIPID CONTENT AND COMPOSITION OF ANIMAL 565 



total fat in man by the determination of total body water. The results of 

 Rathbun and Pace 186 on eviscerated guinea pigs and of Da Costa and Clay- 

 ton 194 on rat carcasses show a close but not perfect inverse relationship be- 

 tween fat and water content when these components are measured by classi- 

 cal analytical methods. 



(e) The Use of Fat-Soluble Indicators. The dilution method would be an 

 ideal procedure for the estimation of body fat if test solutes could be em- 

 ployed which were soluble only in fat. However, from a practical stand- 

 point, since such compounds must be distributed by the blood, it has been 

 necessary to employ compounds preferentially soluble in fat but which are 

 also somewhat soluble in water and fat-free cells. 



Nitrogen and helium gases have been employed as such test substances. 

 According to Shaw and co-workers, 242 nitrogen gas is about five times as 

 soluble in fat as in water; the amount of nitrogen gas eliminated by sub- 

 jects breathing oxygen over a period of six to twelve hours has been shown 

 by Behnke, Thomson, and Shaw, 243 and by Behnke, 244-246 to yield values 

 for body fat of the correct general order of magnitude. 



Cyclopropane constitutes a more practical compound as a fat diluent 

 than does nitrogen or helium. Thus, Lesser and associates 247 reported that 

 good agreement could be obtained between fat calculated from the quan- 

 tity of cyclopropane disappearing in a closed system respirometer and 

 from ether extraction of the tissues. Equilibrium required 1.5 to 2.5 

 hours. 166 



(2) The Normal Fat Content of Man and Animals 



The results of body composition which have been determined on man are 

 summarized in Table 7. 



The analyses of the composition of a man thirty-three years old, based 

 upon data of Bischoff as corrected by Voit and cited by Vierordt, 248 and 

 recalculated by Keys and Brozek 166 are as follows for total solids and fat, 

 respectively, in percentage of wet weight: skeleton, 12.6, 3.8; voluntary 



242 L. A. Shaw, A. R. Behnke, A. C. Messer, R. M. Thomson, and E. P. Motley, Am. 

 J. Physiol., 112, 545-553 (1935). 



243 A. R. Behnke, R. M. Thomson, and L. A. Shaw, Am. J. Physiol, 114, 137-146 

 (1935). 



244 A. R. Behnke, U. S. Naval Med. Bull., 35, 219-240 (1937). 



245 A. R. Behnke, Harvey Lectures, 37, 198-226 (1941-1942). 



246 A. R. Behnke, Medicine, 24, 359-379 (1945). 



247 G. Lesser, A. G. Blumberg, and J. M. Steele, Am. J. Physiol, 169, 545-553 (1952). 



248 H. Vierordt, Daten und Tabellen fur Mediziner und Arzte, 1st ed., Fischer, Jena, 

 1888. 



