A Neiv Conception of the Glomerular Function. 591 



of Miss Cullis upon secretion in the frog's kidney * or to the results I have 

 briefly described above upon secretion in the rabbit's kidney after division of 

 the spinal cord. As is seen from what I have stated, the fact that the 

 glomerulus pulsates has but little bearing, if any, upon its work in propelling 

 the secreted water along the tubule. That pulsation is unimportant in the 

 propulsor action of the glomerulus is borne out by the fact that the urine 

 flows quite freely along the ureter of an excised kidney perfused with fluid 

 at constant pressure, and if in these cases the perfusing fluid be of correct 

 composition, the kidney presents at the end of the experiment appearances 

 exactly comparable to those found by Mackenzie and myself after active 

 diuresis in the intact animal. It is possible that pulsation may play a part 

 in producing the primary dilatation of the convoluted tubule. In an artificial 

 schema representing the glomerulus and tubule, I have found that the volume 

 of fluid driven along the capillary tube by a pressure made to vary in imitation 

 of the pulse variations is exactly the same as if a steady pressure at the mean 

 height of the varying one is used. This indeed was to be expected from 

 theoretical reasons. The value of a varying pressure only arises when the 

 tubule along which the fluid is to be driven has first of all to be expanded. 



In conclusion, then, we may summarise what I have said in the following 

 way : — 



The glomerulus is a secreting surface whose chief function is to secrete the 

 main bulk of the water of the urine, but it is also thrown into activity by 

 such substances as salts, urea, dextrose and caffeine. Its highly characteristic 

 shape is to enable it to act as a means of setting up a pressure-head sufficient 

 in amount to drive the secreted water down the long urinary tubule. The 

 pressure originating from this is also transmitted in some degree through 

 Bowman's capsule to the general tissues of the cortex, thereby exerting a 

 pressure upon the external surfaces of all the tubules lying in the cortex. 

 To what degree the pressure on the external surfaces of the convoluted and 

 other tubules lies below the glomerular capillary pressure I am not yet able 

 to state definitely. The fact that the convoluted tubules show such marked 

 evidences of having been subjected to a high internal pressure certainly 

 indicates a considerable diminution. I have also given reasons for believing 

 that the general pressure conditions so typical of the cortex are non-existent 

 in the medulla ; there, apparently, the internal pressure acts upon the loops 

 of Henle in undiminished amount, and must be supported either by the 

 basement membrane of those tubules, or by the general tissue of the medulla 

 itself. At present the former seems the more probable. Lastly I have given 

 evidence attained by the application of yet another method, which enables us 

 * ' Journ. of Physiol.,' 1906, vol. 34, p. 250. 



