560 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



tissues in proportion to their water content. 197-199 A number of workers 

 have employed this compound as a solute for such estimations, 195,200 ' 201 al- 

 though an equal number 202-204 refused to use it on the basis of an assump- 

 tion, 205 and a report 206 that the distribution of urea between blood cell and 

 plasma water is not exactly equal in the postabsorptive state. 207 However, 

 Keys and Brozek 166 express the opinion that, in all probability, urea may 

 serve satisfactorily as a solute, inasmuch as: (a) although the distribution 

 of urea between cells and plasma is not exactly unity in the postabsorptive 

 state, it is highly constant, and is the same in men and in women, (6) there 

 is no proof that added urea might not have a distribution ratio of unity in 

 the blood, (c) there is no evidence that urea is unequally distributed in the 

 water of tissues other than blood, and (d) no critical tests have actually been 

 made on the validity of water estimates based upon the results of the ad- 

 ministration of urea. In more recent tests with ordinary urea, 207 and with 

 A/ 15 -labeled urea, 208 this substance was shown to yield reasonable values 

 when applied to man ; the results agree with the data obtained by the use 

 of heavy water. It is reported that the urea space is slightly less than that 

 obtained with deuterium water, but this is to be expected in view of the 

 deuterium (hydrogen) exchange in the body. 



(&') Deuterium Oxide (Heavy Water). — The use of deuterium oxide as 

 an ideal test substance for determining the total body water was first pro- 

 posed by Hevesy and Hofer. 209 A number of workers 202 ' 210-214 have era- 



197 E. K. Marshall, Jr., and D. M. Davis, J. Biol. Chem., 18, 53-80 (1914). 



198 K. L. Gad-Andresen, Biochem. Z., 116, 266-302 (1921). 



199 E. E. Painter, Am. J. Physiol, 129, lU-7^5 (1940). 



200 E. M. Widdowson and R. A. McCance, Effect of Undernutrition and of Posture on 

 the Volume and Composition of Body Fluids. Med. Research Council (Brit.), Spec. Rept. 

 Ser. No. 275, 165-174 (1951). 



201 H. L. Kornberg and R. E. Davies, Nature, 169, 502-503 (1952). 



202 N. Pace, L. Kline, H. K. Schachman, and M. Harfenist, J. Biol. Chem., 168, 459-469 

 (1947). 



203 M. F. Levitt and M. Gaudino, Am. J. Med., 9, 208-215 (1950). 



204 B. B. Brodie, Methods in Medical Research, Vol. 4, Year Book Pub., Chicago, 1951, 

 pp. 31-38. 



208 J. P. Peters, Harvey Lectures, 83, 112-142 (1937-1938). 

 2 °s J. O. Ralls, J. Biol. Chem., 151, 529-541 (1943). 



2 ° 7 M. G. Eggleton, /. Physiol, 115, 482-487 (1951). 



2 ° 8 A. San Pietro and D. Rittenberg, /. Biol. Chem., 201, 445-455 (1953). 



209 G. Heresy and E. Hofer, Nature, 184, 879 (1934). 



210 E. J. McDougall, F. Verzar, H. Erlenmeyer, and H. Gaertner, Nature, 134, 1006- 

 1007(1934;. 



211 E. Swift, Jr., J. Am. Chem. Soc, 61, 198-200 (1939). 



212 F. D. Moore, Science, 104, 157-160 (1946). 



213 G. Hevesy, Radioactive Indicators. Their Application in Biochemistry, Animal 

 Physiology, and Pathology, Interscience, New York-London, 1948. 



214 J. D. Hardy and D. L. Drabkin, J. Am. Med. Assoc, 149, 1113-1116 (1952). 



