CHAPTER 1 



PRINCIPLES OF TRACER METHODOLOGY 



Direct Movement of Organisms, Elements, and Compoiinds. Gross Rates of 

 Movement. Some Quantitative Aspects — Concept of Specific Activity; Deter- 

 mination of Ion Movement under Conditions of No Net Mass Transfer; A Substitute 

 for Difficult Chemical Analysis; Isotope Dilution: Volume determinations; Contribu- 

 tion of two sources to a product; Application to analytical chemistry; Modifications of iso- 

 tope dilution; The Kinetic Approach: Simple removal from one phase; Radioactive 

 decay — composite curves; Simple accumulation in one phase; Simple turnover — no return 

 of labeled substance; Turnover or exchange — return of labeled substance; Reversible 

 exchange into more than one compartment; Transfer between phases — precursor relation- 

 ships; General considerations. Metabolic Pathways — Biosynthesis. Advantages 

 OF Double Labeling. Miscellaneous Applications — Bioassays; Steric Rela- 

 tions and Enzyme Action; Radiocarbon Dating; Criteria for Blood Preservation; 

 Study of Rooting Patterns. 



The atom consists of a nucleus or central core, about which revolve 

 particles called electrons. The mass of the atom resides primarily in the 

 nucleus, which for present purposes may be pictured as comprised of par- 

 ticles called protons, having a positive charge, and neutrons, having no 

 charge. In the neutral atom, then, the charge on the nucleus, called the 

 atomic number, will equal that of the extranuclear electrons. The chem- 

 ical and biological properties of an element are determined by the number 

 of extranuclear electrons and therefore by the atomic number, so that an 

 element may be defined as a form of matter all atoms of which have the same 

 nuclear charge. The atomic number is usually designated by means of a 

 subscript at the lower left-hand corner of the chemical symbol: carbon, eC. 

 The subscript is frequently omitted, since the designation of the chemical 

 element suffices to identify the atomic number. The mass number of the 

 atom, which corresponds to the total number of neutrons and protons, is 

 designated by means of a superscript: C^-. The atoms of a given element 

 may have different numbers of neutrons in the nucleus, so that the masses 

 may be different, but the nuclear charge, the atomic number, and there- 

 fore the chemical identity are unchanged. These atoms of the same 

 element but of different atomic weights or mass numbers are called 

 isotopes and are designated symbolically as above, for example, C'- and 

 C^^ Some naturally occurring elements contain atoms of only one mass, 



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