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A working basis is developed for the simultaneous measurement, by means of an isotopic or other label, of all transfer rates of a given chemical element in systems where its transfer between spatially separate compartments of the system must occur by way of a central compartment (mammillary systems). In addition to the measurement of all rates of transfer, the amount of the element within each compartment of a mammillary system can be determined from the same experimental data. The method is applicable in open as well as closed mammillary systems which may or may not be in a state of dynamic equilibrium, and in which rapid uniform intermixing of the element does not occur in peripheral compartments. A basis for the determination of the total rates of appearance and disappearance of multiatomic as well as monatomic substances in any compartment of a system of compartments is presented, without exchanges being restricted to mammillary or other constrained systems. However, only in compartments where chemical transformation of such molecular substances does not occur can the calculated rates of appearance and disappearance of the metabolite be interpreted as rates of transfer into and out of the compartment. Specific problems relating to the tracer measurement of transfer rates in the mammillary systems of living organisms are considered, and a check list is presented for evaluating published experimental results involving tracers as potential sources of information on transfer rates in biological systems determined by means of the above bases for calculation.
Gerald A. Wrenshall (1955) studied this question.