608 On Changes in the Glomeruli and Tubules of the Kidney. 



These two tables bring out the following points : — 



(1) The external diameter of the proximal convoluted tubule does not 

 change on activity ; 



(2) A large lumen is developed in this tubule during diuresis. It varies 

 with the degree of diuresis, and is markedly increased by obstruction of the 

 ureter. Taking the average of all our observations it amounts to nearly 40 

 per cent, of the total diameter of the tubule ; 



(3) The distal convoluted tubule is expanded considerably (from 140 

 to 150 per cent, of its mean at rest) ; and 



(4) The lumen, of considerable size (42 - 3 per cent, of the total diameter) 

 even in a resting kidney, is more than doubled, and becomes 69 '2 per cent, 

 of the total diameter. 



We may conclude, then, that the first convoluted tubule, i.e. that portion 

 which is subjected to the highest internal pressure, is relatively inextensible 

 transversely. The second convoluted tubule, on the other hand, is trans- 

 versely extensible. From a further examination of our sections, we judge 

 that the proximal convoluted tubules do indicate an extension in the longitu- 

 dinal direction, but our present methods do not allow us to state this 

 decisively.* All the results indicate that an internal pressure has existed 

 during diuresis. 



Conclusions. 



Measurements of the diameters of the various portions of the renal tubule 

 in the cat, when at rest and after diuresis under various conditions, show 

 that Bowman's capsule, the glomerulus, and the second convoluted tubule are 

 extensible structures, and are expanded during diuresis. The glomerulus 

 leaves the capsule wall, a considerable accumulation of secretion being found 

 between them. The lumina of all parts of the tubule become greatly enlarged. 



All the appearances found are explained as resulting from the action of a 

 high pressure in the fluid secreted by the glomerular epithelium, and are all 

 in accordance with the propulsor theory of the action of the glomerulus. 



* If we may make the assumption that the volume of the cells of the convoluted 

 tubule does not alter during diuresis, then the magnitude of the surface areas of the 

 cells in a transverse section of the tubule gives us an indication of any change in length. 

 If, for this purpose, we examine the results of Experiments 10, 11, 12, and 13, where vre 

 have direct comparisons of active with resting kidneys, we find that in all instances the 

 proximal convoluted tubules are markedly stretched longitudinally. In Experiments 10 

 and 13 there is considerable shortening of the distal convoluted tubules, and in 

 Experiments 11 and 12 slight shortening. In Experiments 10 and 13 the blood-pressure 

 was high and the diuresis good. In Experiments 11 and 12 the blood-pressure was lower 

 and the diuresis only moderate. Hence it would appear that, with a high internal 

 pressure, this portion of the tubule is shortened, i.e. tends towards the spherical shape. 



