To the Editor:—
In studying the behavior of the plasma volume during diuresis it is apparent that changes in the plasma volume will depend for their magnitude on the intensity of the diuresis in proportion to the volume of the plasma. To illustrate the superiority of the edematous dog to the edematous cardiac patient for experimental purposes in this respect, I give the following approximate average values taken from the recently published paper of Swigert and Fitz (The Journal, Nov. 23, 1940, p. 1786) and the papers of Bryan, Evans, Fulton and Stead (Arch. Int. Med.55:735 [May] 1935) and Evans and Gibson (Am. J. Physiol.118:251 [Feb.] 1937):It may be inferred that trebling the flow of urine when the plasma volume is 3,000 cc. may place no burden on the equilibrium between the tissue fluids and the blood, whereas increasing the flow of urine fourteen fold and to a higher rate with a plasma volume of only 1,000 cc. would affect that equilibrium and produce demonstrable and consistent changes in the plasma volume.