1922] ** Renal Portal”? System. 139 
In other words, increase of pressure, whether it arises in the aorta 
or the post-caval, always has the same effect on the urine.' 
This easily demonstrable fact proves conclusively “that (1) 
absorption in the tubule does not take place; that (2) glome- 
rular filtration must, on this account alone, be deemed a myth ; 
and (3) that therefore the whole of the urine is excreted by the 
tubules—the only possibility left. 
(4) The Secretion of eo bseioy solely is esent or present in Excess in 
the a fen boson Vei rh the Frog when the Fluid Pressure 
— A fferent V eins t8 sinadion relative to the 
ressure in the Arterial Fluid. 
As I have nae in Part I, it is possible with correct 
relative flows in the renal afferent veins and the renal arteries 
to perfuse indigo-carmine dye, potassium ferrocyanide and 
other substances through the renal afferent veins without these 
substances appearing in the urine, but if the renal afferent vein 
p e 
pressure (relative to the pressure in the pa adaaet ad come 
these substances at once begin to appear in the urine. We hav 
also seen in Part II] that the slight excess of Asis in the 
renal afferent vein of one kidney due to the ligaturing of the 
other renal afferent vein is also sufficient to cause the nitrogen - 
richer venous blood to produce urine stronger in nitrogen. 
Since the pressure in the glomeruli cannot be much less than 
29 ems. and if we assume that the pressure in the renal venous 
meshwork and intertubular plexus is as much as 10 cms., it is 
impossible to suppose that a rise of pressure in the renal venous 
meshwork and intertubular plexus of 1-3 ems, is sufficient to 
force the venous blood into the glomeruli (and so to cause the 
dye, ferrocyanide and excess of nitrogen to be filtered from 
the glomeruli) in view of the fact that the patch Reade 
tion remains in full force and at a pressure at least s. (of 
per! higher than that in the intertubular vateth oer if 
his be an impossible supposition, the only alternative is to 
peer that the tubules secrete the urine. I can conceive of 
no possible answer to this argument (more iad stated on 

(12) state ans when the ureter is slightly constricted the urine excreted 
also contains excess of water (less nitrogen) and salt, but this secretion 
urine resulting is as rich in nitrogen as normal urine, and this is of co 
due to the pressure (the arterial blood supply being esse) in the ner 
tubular capillaries being as low as in the normal kidne 
