1922.] ‘* Renal Portal ”’ System. 99 
drives the venous fluid from the intertubular plexus (which, 
according to current opinion, is sacar ass by both the arterial 
and the venous blood or fluid) into the glomeruli, the reply is 
that this alternative cuppomeets is rinipoaslbts when the consid- 
erable difference of pressure which exists between the blood 
in the glomeruli and the blood in the intertubular plexus is 
taken into account. As J shall show in Part III, even the slight 
increase Of blood pressure and flow produced in one renal 
afferent vein by the ligaturing of the companion renal afferent 
vein in a livin ng frog is sufficient to increase the nitrogen-con- 
tent of the urine secreted by the kidney retaining its venous 
supply, and in this case (and in many of my perfusion experi- 
ments) it is incredible that the blood in the intertubular plexus 
(usually said to be at about half the pressure in the glomeruli, 
i.e. about 10 cms; in reality it is much lower than this) could 
the increase of blood pressure above normal in the renal afferent 
vein amounted to as much as 2 cms. No physiologist has ever 
suggested that glomeruli can be injected with a pressure of 2 
cms. above the normal (say 12 cms.) from the renal afferent 
veins while the arterial circulation is in full force, and indeed it 
requires at least 10 cms. pressure to effect this when the arteries 
are empty (4). The suggestion then that excess of nitrogen or 
because the venous blood or fluid has begn forced into the 
glomeruli cannot be entertained for the simple reason that it 
is physically impossible. 
Apart however from the impossibility, examination of 
sections of kidneys perfused with indigo-carmine via the renal 
the urine was a distinct blue, the kidney was found to Ke well 
injected with the dve, but this was restricted to the renal 
