Total body, Erythrocyte and Serum potassium changes during haemodialysis were studied on 29 occasions in 15 patients on maintenance dialysis with a low dialysate potassium concentration (1 mEq/l). The loss in total body potassium during haemodialysis (measured with a whole body counter) varied widely and was significantly related to the pre-dialysis body potassium state of the patient as assessed by total body potassium per kg body weight in spite of a constant high serum to dialysate concentration gradient in all patients. Serum potassium levels did not correlate well with changes in total body potassium or erythrocyte potassium. Erythrocyte potassium was shown to be a reliable and useful index of the direction and magnitude of changes in total body potassium during haemodialysis.

SUMMARY Absorption of calcium from the gastro‐intestinal tract was studied by a new and simple method, combining the use of Ca47, a gamma‐emitting isotope of calcium, and a whole‐body counter. The physical characteristics of the isotope and the design and efficiency of the whole‐body counter are described. The results of 86 studies carried out on 53 subjects with normal or disturbed calcium metabolism are presented. Absorption of Ca47 as estimated by whole‐body counting correlated well with the clinical state and experimental condition. The advantages and disadvantages of the technique are briefly discussed.

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An empirical method is given which may be used for the automatic computation of isodose charts by a high-speed digital computer with an attached digital plotter. The basic physical data is derived from published tissue-air ratio tables. The procedure is valid for the principal axes of rectangular fields, with and without wedges of constant slope, for heams of radiation from a 4 hlv linear accelerator, from 60Co units or in the H.V.T. range 1-3 m m Cu for diaphragm-limited fields. For oblique incidence of radiation on a surface of arbitrary shape, a correction procedure equivalent t o the 'effective S.S.D.' method is used, and a procedure is given to estimate the approximate depth-dose in the presence of internal inhomogeneities of the body.