596 FRED M. tlBER 



direct conversion of oxygen to carbon dioxide in the lungs has been 

 shown experimentally, and O^* has been employed in an effort to 

 determine the source of oxygen in the photosynthetic reaction (see 2, 

 p. 568). 



5. Sulfur 



Stably bound sulfur isotopes have been employed to follow the 

 transport of sulfur compounds in plants {25). The synthesis and 

 metabolic behavior of methionine have been the object of several in- 

 vestigations, both with radioactive S^^ {17, p. 205) and with the 

 stable S34 {27, p. 151). In fact both C^^ and S^^ labels were used to 

 mark methionine. Cystine has also been synthesized and studied 

 with S35 {30). 



References 



GENERAL 



1 . Symposium : Preparation and Measurement of Isotopic Tracers. Ed- 



wards, Ann Arbor, 1946. 



2. Symposium: The ]\Iass Spectrometer as an Industrial Tool. J. Ap- 



pliedPhys.,l3y525{lM2). 



3. Symposium: TJie Use of Isotopes in Biology and Medicine. Univ. Wis- 



consin Press, Madison, 1948. 

 3a. Stewart, D. W., "Mass Spectrometry," in Physical Methods of Organic 



Chemistry, 2nd ed., A. Weissberger, ed., Interscience, New York, 



1949, Chap. XXXI. 

 3b. Hevesy, G., Radioactive Indicators. Interscience, New York, 1948. 



MASS SPECTROMETERS 



4. Nier, A. 0., Rev. Sd. Instruments, 11, 212 (1940); 18, 398 (1947) (con- 



struction details of 60° model). 



5. Brown, H., J. J. Mitchell, and R. D. Fowler, Rev. Sd. Instruments, 



12, 435, 556 (1941) (180° type; electronic control circuits). 



6. Taylor, J. E., Rev. Sd. Instruments, 15, 1 (1944) (60° permanent magnet 



model; C^^ separation). 



7. Washburn, H. W., H. F. .Wiley, S. M. Rock, and C. E. Berry, Ind. Eng. 



Chem., Anal. Ed., 17, 74 (1945) (180° instrument with automatic 

 recording). 



8. Nier, A. 0., C. M. Stevens, A. Hustrulid, and T. A. Abbott, J. Applied 



Phys., 18, 30 (1947) (60° leak detection type; permanent magnet). 



