Glomeruli and Tubules of the Kidney accompanying Activity. 597 



Convoluted tubules — 



Proximal. External diameter ... 



Lumen 



Distal. External diameter ... 



Lumen 



41-4 

 00 



21-2 

 7-2 



41-4 

 17-6 

 32-4 

 20-6 



Weight of K. kidney 

 „ L. kidney 



grm. 



10-9 

 16-2 



These figures show most clearly how extensive a change in size of the 

 different parts of the renal tubule occurs when it is thrown into activity. 

 Thus the capacity of the capsule is more than doubled (to 232 per cent.), 

 chiefly because of the very large accumulation of fluid which has been 

 secreted. The glomerulus is, however, increased to 136 per cent, of the 

 volume of the glomerulus at rest. The differences are in reality still more 

 marked, for a glomerulus actually at rest has no space between the glomerulus 

 and the capsule wall, whereas in the right kidney of this animal no less than 

 7 of the 10 capsules measured contained fluid, though but small in amount. 



We may conclude, then, that both Bowman's capsule and the glomerulus 

 are distensible structures, and, further, that during activity the glomerulus 

 does not remain in contact with the capsule wall, all of which strongly 

 opposes the filtration theory of glomerular activity. These two conclusions 

 are confirmed by every experiment we have performed. 



When we turn to the measurements of the tubules the changes are equally 

 striking. The external diameter of the proximal tubule is usually unaltered, 

 but, whereas the resting tubule has no lumen, the tubule after action has a 

 large lumen (43 per cent, of the total diameter). With the distal convoluted 

 tubule the case is somewhat different. The total diameter is markedly 

 increased (to 153 per cent.). The lumen of the resting tubule is 34 per 

 cent., but that of the active tubule 64 per cent, of the total diameter of the 

 tubule. Also, the lumen of the active tubule is 2 - 86 times greater than that 

 of the resting. Apparently, then, the basement membrane of the proximal 

 convoluted tubule is practically inextensible with the forces at play in this 

 instance, whereas that of the distal convoluted tubule is extensible. In 

 both tubules the cells are distinctly flattened against the basement membrane 

 as a result of activity. 



II. Comparison between a Resting and a Decapsulated Kidney. 



The measurements obtained in an experiment of this character (Experi- 

 ment 11) were as follows : — 



