1922 } « Renal Portal” System. 97 
pressure in the intertubular plexus, being inversely propor- 
tional. In another series: of experiments (Appendix B) I 
ascertained that 0°025% of potassium ferrocyanide present in 
the renal afferent vein fluid alone did not appear in the urine, 
and that with ferrocyanide present in both arterial and renal 
afferent vein fluids, excess of strength of the latter up to three 
times that of the arterial fluid had no effect on the urine.'! In 
a final experiment in which the following three fluids were 
employed :— 
Aortic aaa gad 8 apm o oa urea, 0° arate ferro. , 0° mae KI. 
*46” i ge , 0°00958% 0-0 i a 
602 2 ae a ze vote, , 001259, -—s * 0.02 ye ie 
the aortic fluid perfusing the vealed arteries during the whole 
experiment, and the three fluids being successively perfused 
through the ‘Wo renal afferent veins, the three samples of 
urine obtained were identical in composition. 
in this as in all other series—the renal afferent vein fluids 
being perfused via the aorta instead of via the renal afferent 
veins—and in all these control experiments the urine composi- 
tion corresponded in strength to the fluid perfused. 
These results thus afford conclusive evidence that the arteri- 
al fluid in the intertubular plexus is the only ‘one concerne 
with the secretion of urine and that with correct (i.e. nor- 
mal) flows, the venous fluid in the renal venous meshwork does 
not enter the intertubular plexus. 
On the pee of a slight Increase of Pressure* above the Normal 
n the Fluid in the Renal epee Veins 
ply) has nothing to do with the secretion of urine. The case 
is very different however if, in these experiments, the renal 
afferent vein perfusion bottles be raised from 1 em.—3 cms. 
in height (according to the amount of deficiency of flow in the 
renal afferent veins below normal, relative to the arterial flow), 
thus increasing the flows of fluid in the renal afferent veins, 
both absolutely and relatively to the flow of fluid via the renal 
arteries. The flow of fluid in the renal afferent veins being 
above normal relative to the flow in the renal arteries, indigo- 


Ferrocyanide estimated colorimetrically by addition of equal 
guantities of a stock solution of ferric chloride. 
