A New Conception of the Glomerular Function. 



587 



logically the tubules within such a collapsed pyramid are observed to be 

 flattened and empty. 



It is possible that some or even all of this compression might be post 

 mortem, but I think that it is ante mortem, since it is only found if sufficient 

 time be allowed to lapse between the ligaturing of the ureter and the removal 

 of the kidney. The longer the interval the more marked is the compression. 

 I think the compression is produced in the following way : — After the ureter 

 has been ligatured urine continues for a time to be expelled into the pelvis, 

 and gradually the pressure there rises. Fluid will continue to be forced 

 into the pelvis' in gradually decreasing volume until the pressure reaches 

 that of the glomerular capillary blood-pressure. The further distension of 

 the pelvis and compression of the medulla is probably produced through the 

 pulsatory variations of pressure in the cortex. The systolic pressure, by 

 the expansion of the glomeruli and arteries, suddenly raises the tension 

 throughout the whole cortex ; this expels a little of the fluid from the 

 terminal portions of the tubules into the pelvis, whose pressure then becomes 

 greater than diastolic pressure. As the pressure falls in diastole a point is 

 reached at which the cortical pressure is below the pressure in the pelvis, 

 that is below the pressure in the fluid contained within the loops of Henle 

 and the collecting tubules. Accordingly these latter are emptied or partially 

 emptied into the cortical tubules, while the lower ends of the collecting 

 tubules are compressed and act as valves, preventing any return flow from 

 the pelvis up the tubule. In this way more and more fluid is gradually 

 collected within the pelvis at the expense of the medulla. 



If, as I think is the case, we may divide the kidney substance into two 

 parts, in one of which the whole tubule is exposed to a considerable pressure, 

 both internal and external, while in the other region the pressure is largely 

 within the tubule, the difference must have some important physiological 

 meaning. It is most significant that the loops of Henle are carried down 

 into this region of low external pressure. In different animals the loops of 

 Henle show many diversities of form, more particularly in length, and it is 

 certainly a striking fact that in some animals the major number of loops are 

 short, and either lie completely within the cortex or only descend into the 

 outermost portions of the medulla. It has been pointed out that the animals 

 with very short loops are those which secrete a dilute urine, whilst those 

 in which the loop penetrates far into the medulla secrete a concentrated 

 urine. Hence it may be that this loop effects a certain amount of absorp- 

 tion, a function which would be aided by a pressure difference acting from 

 within the tubule. 



To test my theory further, and in the hope of gaining some evidence of the 



VOL. LXXXVII. — B. 2 Y 



