1922.] ‘** Renal Portal”? System. 141 
Since in my opinion the evidence submitted under the 
preceding five headings constitutes absolute proof of the truth 
of the Tubule cum Rete theory, I do not propose to offer 
further original evidence nor to call to mind the large volume 
of other evidence which has already been advanced by previous 
investigators 
Alternative Hypotheses to account for the Enclosure of the 
Glomerulus in the Capsule, 
From the standpoint of zoo-physiology there is but little 
need to adduce evidence in support of the assertion that, while 
the large diameter and short length of the renal artery allows 
a large volume of blood to supply the kidney at high pressure 
and rapid rate of flow, the function of the glomerulus is to 
reduce this pressure and retard this rate of flow to appropriate 
values, while maintaining a volume of blood which is relatively 
large compared with that supplied to other glands. Glands far 
removed from a seat of high pressure are usually intermittent 
in action and when functional depend for a temporarily in- 
creased volume of blood on local vaso-dilatation, the length of 
artery separating them from the aorta ensuring low pressure 
and slow rate of flow. But the kidney, on the other hand, is 
continually and intensely active and thus needs a constant 
large volume of blood in its vessels and this can best be secured 
by proximity to the aorta provided that it is shielded against 
t i ) 
proximity involves. The glomeruli are thus to be regarded 
as the physiological equivalents of the length of artery which 
separates most glands from the seat of maximum pressure and 
this is the normal function of most kinds of known retia 
mirabilia, of which the glomerulus is but one example. In short 
the glomeru lus is the equivalent of a wateriall in the course of 
a large river near its mouth, the fall obliterating or minimizing 
the ‘‘ pressure head ”’ and the rate of flow, while maintaining 
arteries which s supply other glands are comparable to small 
tributaries of the river near its source in w ich the volume of 
water is small and the “‘ pressure head ”’ and rate of flow not 
necessarily very large. In both cases the pressure and rate of 
flow may be about the same, but the volume of water at the 
base of the fall is enormously greater than the volume of water 
in a tributary, and the latter can only be increased in the 
tributary i the widening of the bed to form a pool. 
e glomerulus differs from ail other known retia 
shakes in that it becomes encapsulated in a glandular tube, 
and it is this feature alone which, not unnaturally has origi- 
nated the idea of the blood in the ‘glomerular capillaries part- 
ing with a portion of its water and some other constituents to 
