Radiosilver (llOmAg) was administered to mice, rats, monkeys, and dogs by oral and intravenous routes and also intraperitoneally to mice and rats. Retention as a function of time was determined by periodic assay in 4~ liquid scintillation detectors. The data were adequately described by exponential expressions. Ninety per cent or more of oral doses were not absorbed. In all routes of administration more than 90% of the silver excreted was in the feces. A parabolic relation between body weights and estimated equilibrium levels in small animals was extrapolated to man. From such estimates an MPC, value of 1.8 nCi/cm3 (when the whole body is the critical organ) was derived. The ICRP value of 0.3 nCi/cm3 for the lower large intestine is still the limiting value.

Direct determination of daily water exchange between the environment and a mammalian organism is conceptually simple but technically difficult because sources other than water per se contribute to the body water reservoir. These sources include food, biological oxidation of hydrogen, and pulmonary and cutaneous exchange with the atmosphere. The practicability of estimating total water exchange solely by means of a tracer, however, has been elucidated and verified by several groups of investigators (Pinson and Langham, '57; Roberts, Fisher and Allen, '58).Pinson and Langham ('57) showed that tritium water (HTO) moves across barriers at the same rate as ordinary water. At any given time, the specific activity of water obtained from samples such as urine or sweat was the same as the specific activity of the body water. Pinson and Langham ('57) also found that after HTO equilibrated with body water, the logarithm of the HTO concentration in the body water decreased linearly with respect to the total accumulated volume of water entering the body water reservoir. When the intake rate was held constant at 2.7 liters per day, the logarithm of the HTO activity was a linear function of time. Roberts, Fisher and Allen ('58) described the functional relation between water intake and intake calculated from studies with deuterated water (HDO). The relation was linear with a slope of one and appeared to have consistent prediction validity within the limits of experimental accuracy. These workers also considered the exchange of body water in terms of the variables necessary to measure inflow and outflow rates for both HDO and HTO, when the body water was constant or changing in volume. The organic binding of tritium which occurs in animals represents only 0.5 to 1.0% of the total administered dose (Thompson, '52) and does not affect the validity of using an isotope of hydrogen to estimate total daily water exchange.As an adjunct to studies on the comparative metabolism of gamma-emitting radionuclides, the kinetics of body water retention were studied with tritium water in 7 mammalian species, including man. It was hoped that these studies on laboratory animals would yield information which would allow one to relate certain metabolic phenomena which occur among mammals on an interspecific basis. Such correlations are of considerable interest to the physiologist and may prove valuable in estimating the metabolic parameters which are used to determine maximum permissible exposure values for radionuclides. METHODS AND MATERIALSTritiated water was administered to 7 species of adult mammals maintained on their normal dietary regimens throughout the experimental period. The usual feeding schedules were followed for dogs, horses, and human subjects, whereas food was available continuously to the mice, rats, rabbits, and Kangaroo rats. With the exception of the single case noted in table 1, all species were allowed water ad libitum. Table 1 gives details of the individual experiments as to species, sex, number of animals, initial body w...

Excretion of menthol (as glucuronide) from orally ingested peppermint oil contained in Colpermin was compared with oil contained in two soft gelatine capsules. Total 24 h urinary excretion of menthol was similar in the two formulations in healthy volunteers, but peak menthol excretion levels were lower and excretion delayed with Colpermin. Menthol excretion was reduced in ileostomy patients who took Colpermin and moderate amounts of unmetabolised menthol were recovered from the ileostomy effluent. This is consistent with Colpermin being a delayed‐ release form of peppermint oil.

Radiomanganese ("Mn) was administered to mice and rats by the oral, intravenous and intraperitoneal routes and to dogs and monkeys by the oral and intravenous routes. Whole-body-counting techniques, utilizing 47r liquid scintillation counters, were used to determine whole-body-retention parameters. Retention functions consisting of the sum of three or four exponential expressions were adequate descriptions of retention until the body burden was less than 1 per cent of the administered dose. The longest effective half-times after intravenous injections were 119, 146, 99 and 68 days for mice, rats, monkeys and dogs, respectively. Tissue distribution studies in rats showed that, for most tissues, concentration as a function of time roughly paralleled whole-body retention. Both bone and brain were found to have a slower rate of loss than other tissues. Using a parabolic relation between body weights and the integrals of the retention functions, it was estimated that 6 x lO-3pc/ml was the maximum permissible concentration in water when the total body is the critical organ. This value is in good agreement with the current ICRP value of 8 x However, the value calculated for the lower large intestine (1 x lop3 pc/ml) must remain the MPC, for 54M~1.

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