XBSTRACT. Traditional methods of carrying out internal-dose calculations are not adequate for the detailed models now in existence, nor for the many types of radionuclides presently in use. A formalism for absorbed-dose calculation is presented which is applicable to all radionuclides and all models. It is based on equations which are derived in general terms, independent of the properties of any single type of radiation. The development of the formalism starts with the concept of absorbed fraction, but a new concept, speci$c absorbed fraction (i.e., absorbed fraction per gramme), is shown to be more widely applicable. The proposed formalism will increase the complexity of dose calculation only under circumstances where traditional methods oversimplify the concepts and distort the result.

The loss of Na22, K42, and Cl36 from single giant axons of the squid, Loligo pealii, following exposure to an artificial sea water containing these radioisotopes, occurs in two stages, an initial rapid one followed by an exponential decline. The time constants of the latter stage for the 3 ion species are, respectively, 290, 200, and 175 minutes. The outflux of sodium is depressed while that of potassium is accelerated in the absence of oxygen; the emergence of potassium is slowed by cocaine, while that of sodium is unaffected. One cm. ends of the axons take up about twice as much radiosodium as the central segment; this difference in activity is largely preserved during exposure to inactive solution. Such marked differences are not observed with radiopotassium. From the experimental data estimates are given of the influxes and outfluxes of the individual ions. The kinetics of outflux suggests a cortical layer of measureable thickness which contains the ions in different proportions from those in the medium and which governs the rate of emergence of these ions from the axon as though it contained very few but large (relative to ion dimensions) pores.