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Prof. T. G. Brodie. 



is of course incomplete, in that it takes no account of the tubular structure 

 and the facts that the pressure is set up in the fluid within the tubules and 

 that the walls of the tubules offer some resistance to expansion. The first 

 effects of the glomerular pressure will therefore be to distend the capsule 

 and the first convoluted tubule, i.e. to increase its lumen, thus offering less 

 resistance to the flow of fluid along the tubule. In this distension the pulsa- 

 tion of the glomerular vessels is probably utilised. Also the more rapid the 

 flow along the tubule the greater the pressure gradient, and the smaller 

 the pressure transmitted through the walls of the tubules to the 

 general kidney substance. We must therefore expect to find a distinct 

 difference between the intratubular pressure and the intra-Capsular pressure, 

 and while fluid is moving down the tubule the two could only be equal at 

 the point where the tubule leaves that part of the kidney substance where 

 the pressure is raised. This region is limited as we shall see by the branching 

 arches of the renal vessels in the intermediate zone. 



There is yet another feature of the renal structure and form which is 

 capable of interpretation by this theory. This is the general shape of the 

 mammalian kidney, so typical as to give its name to all structures in any 

 way resembling it. The kidney is very typically constructed of a cortical 

 mass enveloping a medullary portion. The blood-vessels form a set of arches 

 between these two parts. My suggestion is that this arched system of 

 vessels forms a more or less rigid base upon which the cortex lies. Conse- 

 quently when, in activity, the pressure in the general renal tissue rises 

 through the activity of the glomeruli it is restricted in the first instance to 

 the cortex. The cortex, so to speak, becomes compressed between the rigid 

 Capsule and the firmly distended arterial arches. From this general pressure 

 the medullary portion is relieved, and it is a most significant fact that the 

 loops of Henle lie within this region, where there is probably but little 

 external pressure. Apparently, then, the difference in state between the 

 tubules in the cortex and those in the medulla is that there is a high 

 pressure on both internal and external surfaces of the tubules lying in the 

 cortex, whereas in the medulla the pressure may be acting chiefly, possibly 

 entirely, from the inner surface of the loops only. In this connection I have 

 frequently observed the following most notable result : — If at the height of 

 a diuresis whilst urine is flowing freely the ureter be ligatured, and after 

 about 20 minutes the pedicle be tied off and the kidney removed, it will 

 be found that the pelvis is widely distended with fluid, and usually the 

 pyramid is compressed towards the cortex until it forms an almost 

 insignificant structure projecting into the cavity of the pelvis. Histo- 



