PHOSPHORUS 281 



containing a standard nutrient solution which was enriched to contain 

 about 10 MC P^' per liter. When the plants were small, 200 ml of nutrient 

 solution was used which was increased progressively up to 1000 ml as the 

 plants grew. The total activity taken up by the plant was estimated 

 from measurements on the nutrient solution at the beginning and end of 

 the experiment. Since the interest was primaril}' in comparing given 

 tissues between different plants, measurements were made directly on the 

 tissues, which were prepared in the same way for each plant and which 

 therefore had about the same self-absorption. Thin cross sections of the 

 roots were cut by hand, and circular or rectangular pieces of leaf were 

 used. Radioactivity was calculated on the basis of area. 



In a study of uptake by bacteria (P-22), P^- as Na2HP04 was used at 

 concentrations of 10^ dis/min/ml of culture medium. The P'- content 

 of the bacteria was estimated by taking 8 ml of the culture, fixing by mak- 

 ing the solution 2 per cent with respect to formaldehyde, centrifuging, 

 washing in 0.8 per cent saline, and counting the pellets with an end- 

 window tube. It was shown that the measured activity was not due to 

 adsorption of P^- on the bacterial surfaces or to residues from the radio- 

 active culture. 



P-l. Rubin, B. A.: A Source of Error in Tracer Experiments with P^^, Science, 110: 

 425 (1949). 



P-2. Koch, Frederick C, and Martin E. Hanke: "Practical Methods in Biochemis- 

 try," 5th ed., The Williams & Wilkins Company, Baltimore, 1948. 



P-3. Fister, Harold J.: "Manual of Standardized Procedures for Spectrophotometric 

 Chemistry," Standard Scientific Supply Corporation, New York, 1950. 



P-4. "Methods of Analysis of the Association of Official Agricultural Chemists," 

 6th ed.. Association of Official Agricultural Chemists, Washington, D.C., 1945. 



P-5. Kleiber, Max, Arthur H. Smith, and N. P. Ralston: Secretion in Cow's Milk 

 of Intravenously Injected Radioactive Phosphorus P^^, Proc. Soc. Exptl. Biol. 

 Med., 69: 354-356 (1948). 



P-6. Lofgreen, G. P., Max Kleiber, and J. R. Luick: The Metabolic Fecal Phos- 

 phorus Excretion of the Young Calf, /. Nutrition, 47: 571-582 (1952). 



P-7. Lofgreen, G. P., Max Kleiber, and A. H. Smith: The Digestion and Absorption 

 of P32 Labeled Casein by the Young Calf, J. Nidrition, 43: 401-412 (1951). 



P-8. Smith, Arthur H., Max Kleiber, Arthur L. Black, Melvin Edick, Robert R. 

 Robinson, and Hubert Heitman, Jr.: Distribution of Intravenously Injected 

 Radioactive Phosphorus (P'^) among Swine Tissues, J. Animal Sci., 10: 893- 

 901 (1951). 



P-9. Kleiber, Max, Arthur H. Smith, N. P. Ralston, and Arthur L. Black: Radio- 

 phosphorus (P^2) as Tracer for Measuring Endogenous Phosphorus in Cow's 

 Feces, J. Nutrition, 45: 253-263 (1951). 

 P-10. Shirley, R. L., J. C. Driggers, J. McCall, G. K. Davis, and N. R. Melirhof: 

 Excretion and Retention of P^^ ^nd Ca"*^ by Laying Hens, Poultry Sci., 30: 

 730-734 (1951). 

 P-11. Patrick, H., and G. K. Schweitzer: Absorption and Retention of Radioactive 



Phosphorus by Chicks, Poultry Sci., 31 : 888-892 (1952). 

 P-12. Hansborough, Louis A., and David Denny: Distribution of Phospliorus'^ in 



