Dynamic equilibrium in a biological system implies that the compartment under study does not change in size during the period of observation. In many biological systems there are, however, net changes with time and this report deals with the mathematical treatment necessary to calculate unequal rates of inflow and outflow.A method is presented for the calculation of transfer rates in a two compartment system when the rates of flow between these compartments are unequal but constant. Equations were developed to calculate the amount of material transported per unit time derived from measurements of specific activity and compartment size.

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Ten healthy volunteers (five males and five females), 25 to 41 years of age, were exposed to several different environmental conditions in a constant temperature room. It was found that at 20 C. and about 55 per cent humidity, about five hours after the last meal, the behavior of the temperature of the toe in contrast to that of the finger was consistent, reliable and reproducible. These conditions, somewhat cooler than those frequently used, were deemed suitable for testing vasodilator drugs or procedures. INVESTIGATION of skin temperature hasgenerally been conducted at environmental temperatures between 23 C. and 31 C. This range represents the approximate limits of the zone of vasomotor regulation or the condition of comfort.'-3 The environmental conditions most often selected have been temperatures from 24 to 27 C., relative humidity of 40 to 50 per cent, and wind velocity of less than 1 meter per second. The subject was generally in the basal state, awake, lightly clothed, and in a semireclining or supine position. Most of the work in this field has been carried out within these limits. '-5 These conditions, however, were found to be unsuitable for testing the effect of vasodilator drugs on skin temperatures, for two reasons: first, the period of time necessary for adaptation was impracticably long and spontaneous variations in temperatures recorded interfered with the interpretation of the curves; second, it was necessary to have the room cool enough to maintain the extremities in gentle vasoconstriction so that dilation of the vessels could be readily recognized.It has been shown that even under carefully controlled conditions within the zone of vasomotor regulation, a period of from one to two