The Renal Blood Flow 75 



when we did this experiment was a change in renal plasma 

 flow, but in this respect the experiment was entirely negative. 

 The slight parallel variations in the diodrast and inulin clear- 

 ances are probably not real fluctuations in activity but errors 

 due to incomplete emptying of the bladder. 



We have in our records a considerable number of such 

 negative experiments, for we have had occasion to examine 

 the action of a number of drugs upon renal function in our 

 search for certain desired effects, and usually this has been 

 the result. But these negative experiments at least enable us 

 to say that the renal plasma flow and filtration rate in a nor- 

 mal individual can be expected to remain quite constant over 

 a two or three hour interval, or for that matter, in repeated 

 examination at widely separated intervals. One subject ex- 

 amined in the basal condition on 12 occasions over a period 

 of 4 months has shown an extreme variation of only — 1 5 

 per cent from the average figure. Assuming a constant basal 

 or resting blood pressure, this fact merely bespeaks the sta- 

 bility of the vascular bed of the kidneys. 



We may go farther than emphasizing the constancy of 

 the renal blood flow in any one individual: it is in fact quite 

 uniform in different individuals. In comparing 34 normal 

 subjects which we have examined in the basal condition up to 

 the present time, the standard deviation, counting each indi- 

 vidual but once, is 1 6 per cent of the mean. The mean value 

 is 737 cc. of plasma, or 1275 cc. of whole blood per minute, 

 which is about one-third of the basal cardiac output. Though 

 this uniformity in renal blood flow is not wholly unexpected 

 on an anatomical and physiological basis, the absolute magni- 

 tude of 1275 cc. has been rather surprising. It is, however, 

 no greater than might be expected from observations on 

 anesthetized animals. 



