The Renal Blood Flow 93 



renal plasma flow equal to the average normal value, and in 

 only three subjects (the 1st, 3rd, and 4th) does it exceed the 

 smallest observed normal value. In the absolute sense all sub- 

 jects show renal ischemia. 



In considering what plasma flow is to be expected in any 

 subject, it will be readily agreed that it is misleading to con- 

 sider the absolute renal plasma flow in a disease which is pro- 

 gressively destroying renal tissue ; if 5 per cent of the kidney 

 were destroyed we would expect the plasma flow to be reduced 

 proportionally, or roughly so; and if the remaining 50 per 

 cent had a normal plasma flow per unit of intact tissue we 

 would, from the experience of unilateral nephrectomy, ex- 

 pect this plasma flow to be physiologically adequate. It is ob- 

 viously more appropriate in a problem such as this to consider 

 not the absolute value of the renal plasma flow but the plasma 

 flow per unit of residual, functionally intact tissue. 



We may take diodrast-Tm, which reflects the quantity of 

 intact tubular tissue, as a basis of comparison, and relate these 

 subjects to each other and to the normal according to the 

 magnitude of this value. To facilitate this comparison graph- 

 ically we have simply drawn three parallel sloping lines from 

 the normal values of renal plasma flow, filtration rate and 

 diodrast-Tm at an arbitrary but convenient angle, and then 

 arranged the subjects in order of decreasing diodrast-Tm. 

 Since these data are plotted logarithmically, this arrangement 

 is such that if one were to reduce all functions in the normal 

 kidney progressively and in a proportional manner, these 

 functions would decrease along these parallel lines. Another 

 advantage of using logarithmic ordinates is that equal linear 

 excursions up or down in any variable represent equal per- 

 centual changes. 



