IN a paper which has recently been published, McCance1 described the effects of administering hypertonic salt by mouth and intravenously to a dehydrated person. Volumes of urine up to 7–8 c.c./min. were passed, and this urine had a much lower osmotic pressure than the urine passed by the same person before the salt was given. The concentration of sodium chloride in the urine, however, appeared to be at or near the maximum concentration of which the kidney was capable, and it was suggested that the reabsorption of water in the distal tubules was being limited by the concentration of sodium chloride reached within them, a maximum value being attained when the osmotic pressure was still below the level at which it would become the limiting factor. It has now been shown that this conclusion was incorrect, and that it is the total osmotic pressure which is the limiting factor all the time, but that its limiting or maximal value is related to the minute volume, and falls as the latter rises. The evidence was obtained by such experiments as the following.
McCance, R. A., J. Physiol., 104, 196 (1945).
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