1922.] ** Renal Portal” System. 147 
encapsulated glomerule occurs in actuality. In the experi- 
ments referred toonp 5 ,in which | first perfused saline plus 
urea via the renal arteries in the frog and obtained a profuse 
secretion and then filled the perfusion bottle with chromic acid 
fixative, so fixing the tissues of the kidney in the act of 
vigorous secretion, | found, on subsequently macerating and 
teasing up the kidney (in Marcace/’s fluid = equal parts of nitric 
aci(l, glycerine and water) that in all cases the glomeruli com- 
certain value, the urine becomes forced back into the capsule 
and the glomerulus becomes contracted.? 
Brodie and Mackenzie (13) come to the couclusion that 
whenever a kidney is active, a space always exists between the 
inner and outer capsule walls, representing, in their opinion, 
the urine which is being exuded from the glomerulus, but this 
spice, observed by these authors, is due either (a) to differen- 
this was the case in my chromic acid experiments) or (6) it is 
due to the fact that these authors “‘ were never able to kee 
the blood in a kidney that was excised at the height of activity. 
At the instant of excision such a kidney is hard and tense, and 
Instantly becomes soft when the first ligature is tied round 
the pedicle. This is even the case though the vein be first 
ligatured...... ven then there is a distinct escape of blood 
through the Capsule [enclosing the whole kidney] and the cortex 
rapidly pales in colour as the tension falls.”” “In other words, 
at excision, while urine secretion by the tubules continues, 
the blood pressure inside the kidney falls and the urine secre- 
tion pressure automatically becoming greater than the reduced 
blood pressure, the urine is naturally forced back into the cap- 
sule.? The int psular sj observed by Brodie and Macken- 




1 The condition of the glomeruli in this latter experiment also shows 
that the swelled condition of the glomeruli of the first experiment was 
no the macerating fluid, as my friend Mr. R. H. Whitehouse 
su : eee its 
2 The contraction of the glomeruli in these reverse current experi- 
ments probably also in part explains why only a proportion of the 
perfusing fluid made its exit from the renal artery or arteries and not the 
A ; 
oO . 
8 Brodie (11, p. 581) admits the possiblity of this explanation and in- 
