In a crossover study in six volunteers over the age of 65, absorption of 500 mL of normal saline given subcutaneously was compared with that given intravenously. Tritiated water and technetium pertechnetate were used as water tracers. Tritium radioisotope levels in the blood increased in a smooth curve during subcutaneous infusion, reaching equilibrium levels within 60 minutes. The area under the curve after subcutaneous infusion was almost identical to that after intravenous infusion in all subjects. Radioactivity could not be demonstrated at the subcutaneous site 1 hour after completion of the infusion. Subcutaneous infusion is an effective method of giving fluid to elderly people and deserves more widespread use.

A fluorescein-labelled antiserum to human Tamm-Horsfall mucoprotein applied to frozen human kidney sections gave strong specific labelling, mainly of cells of tubules in the outer medulla. By comparison with adjacent serial sections stained for alkaline phosphatase and succinic dehydrogenase, it is suggested that material reacting immunologically as Tamm-Horsfall muco-protein is found particularly in the cells of the ascending limb of the loop of Henle and the macula densa segment of the distal tubule.

SYNOPSISThe factors determining aggregation of Tamm-Horsfall urinary mucoprotein have been examined using the technique of light-scattering photometry, which has allowed the study to be performed at the concentrations of the mucoprotein in which it occurs in the urine in vivo.The tendency to formation of aggregates is enhanced by increases in concentration of the mucoprotein, by increases in electrolyte concentration within physiological limits, and by lowering of the pH within the physiological range. The effects of 1:2 and 2:1 electrolytes are somewhat different from those of 1 :1 electrolytes. The data suggest that the isoelectric point of Tamm-Horsfall protein is higher than previously thought.

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SYNOPSISThe composition of hyaline casts has been investigated. The major constituent appears to be the urinary mucoprotein described by Tamm and Horsfall. Small amounts only of serum proteins are present.Neither the amounts excreted nor the concentration of Tamm-Horsfall protein appeared to determine the rate of cast formation. The only invariable association of hyaline cast formation was with the presence of significant amounts of serum proteins in the urine.In vitro it was found that aqueous solutions of serum albumin were particularly effective in producing precipitation of Tamm-Horsfall protein. This interaction was inhibited in normal urine but occurred to a greater extent in nephrotic urine and is suggested as the possible mechanism of hyaline cast formation.