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Potassium-42 was used as a tracer of the total exchangeable body potassium in six cows and five large sows. One millicurie of K42solution was injected intravenously into each animal and samples of urine and faeces were collected in 8-liter plastic pails, at intervals, for 70 hours. The radioisotope content of the samples was determined by dipping an unshielded sodium iodide scintillometer into the pails to a constant depth. Background error was reduced by setting the discriminator levels to accept only pulses corresponding to the photopeak of the K42emission. The rate of excretion of K42decreased for approximately 16 hours, then appeared to remain constant for the rest of the experiment. Means of biological half-life values, as calculated for the period from 22 to 70 hours, were 10.5 days for the cows and 45.6 days for the pigs. Percentages by weight of total potassium in the animals were 0.21 for the cows and 0.24 for the pigs, as estimated from flame photometric determinations of urinary potassium and biological half-life values. These results are compared with caesium and potassium studies reported by other investigators.

Toronto General Hospital records show that 26 persons received Thorotrast myelography in the years 1940 and 1941. Of these, 15 have been located and the activity in nine has been measured for residual thorium activity using a whole-body counter and thoron exhalation techniques. For comparison, measurements of thorium burdens of nine subjects who had Thorotrast arteriograms are presented. Of the 15 myelography cases located, 12 have had serious progressive cauda equina deficit. Even on the assumption that the 11 unlocated are all well, the incidence of myelopathy is still nearly 50 per cent. On certain assumptions the thorium burdens of the nine measured are ascertained to be between 0·03 and 1·0 g, with a mean value of 0·45g. It is pointed out that these levels are all comparable to, and in some cases less than, the maximum permissible body burdens (ICRP) and yet severe effects have occurred.

Using a scintillation spectrometer, measurements have been made of the distribution of potassium and radioactive caesium in the bodies of the cow and the pig as a result of the ingestion of these materials. The results of these experiments, which are based on measurements of the radioactivity normally found in foodstuffs and in animals, agree with those of earlier experiments in that there is no great concentration of Cs137apparent in any one organ. However, there is evidence for preferential concentration in the kidney and testes.

An investigation has been made of the gamma-ray activity of foodstuffs eaten by Toronto residents in the spring of 1959, and a comparison made with the activity of the residents themselves. From this, it is calculated that the Cs-K discrimination ratio, (Cs/K)food: (Cs/K)body, is 1:3.