90 Physiology of the Kidney 



that in no appreciable number is the blood flow substantially 

 below the average.''* 



Summarizing this portion of this paper, the picture which 

 we have of the normal human kidney is an organ composed 

 of a million-odd nephric units, each presumably capable of 

 functioning more or less independently of the other, in which 

 the blood flow, both glomerular and tubular, is determined by 

 the autonomous activity of the glomerular apparatus or other 

 local vascular devices; connection with the autonomic ner- 

 vous system is unnecessary for the maintenance of local 

 renal constrictor tone, and the autonomic nervous system 

 contributes little if anything to the regulation of renal 

 blood flow under basal, resting conditions. The two kid- 

 neys normally receive about one-third of the total cardiac 

 output. The renal blood flow can be substantially reduced 

 by adrenin and by reflex vasoconstriction, and it can be in- 

 creased during the pyrexial reaction, the maximal renal blood 

 flow being perhaps 100 per cent above the basal value. In 

 spite of the fact that the basal renal blood flow is only about 

 half of the apparent maximal value, it appears that all the 

 glomeruli and tubules are active in the basal condition, in 

 that the number of functioning units, either from the point 



"'■ In all ooir present observations the load of glucose and diodrast delivered to the 

 tubules is considerably in excess of the minimal load required to effect saturation when 

 the latter is evaluated in terms of the average filtration rate and plasma flow for all 

 nephrons. By reducing the plasma levels of glucose and diodrast towards the critical 

 levels slight variations in filtration rate and tubular blood flow would be revealed, but 

 we have preferred in the first instance to work under conditions suitable for the detection 

 of more marked ischemia. For a discussion of the quantitative limitations of these satura- 

 tion methods the reader is referred to the footnote on page 32. The above results 

 controvert the belief that perhaps as many as 40 per cent of the glomeruli in the human 

 kidney are wholly or nearly active at any one moment. This belief had its origin in no 

 experimental evidence, so far as man or mammals are concerned; but the organization of 

 the frog kidney is in many respects very different from that of the human kidney, and the 

 observation rests solely upon the fact that the frog kidney shows alternation of glomerular 

 activity cannot be transferred from frog to man with any rational justification. 



