Glomeruli and Tubules of the Kidney accompanying Activity. 595 



to a sphere whose diameter was the mean of the two diameters of the capsule. 

 The figures representing volumes given in this paper were obtained by cubing 

 the mean radius of the capsule expressed in microns, and dividing it by 1000. 

 Hence, to convert the figures into cubic millimetres, they must be multiplied 

 by -J^xlO -6 . The glomerulus was also compared to a sphere, whose 

 diameter was the diameter of the capsule minus the maximum space between 

 the glomerular surface and the capsular surface. The difference between the 

 two volumes thus ascertained gives us an approximate estimate of the 

 volume of the fluid contained within the capsule. 



In measuring the tubules a section of a proximal convoluted tubule lying 

 near to the glomerulus was selected, and that section of the distal convoluted 

 tubule which lies close to the point of entrance of the vessels into the 

 glomerulus. Hence the proximal tubule probably belonged to the glomerulus 

 measured, and the distal tubule certainly did so belong. 



I. Comparison between a Besting and an Active Kidney. 

 A. The Glomerulus and Capsule. — There are always marked differences 

 between a resting and an active glomerulus. A resting glomerulus appears 

 to be made up of a dense tissue closely packed with nuclei (fig. 1). The 

 glomerular surface always lies in contact with the capsule wall, and the 

 whole structure is usually irregularly quadrangular in outline. After 

 activity the glomerulus stands away clearly from the capsule. The outline 

 of the glomerulus is lobular, and in structure it is much looser than the 

 resting glomerulus (fig. 2). It also appears to be filled with large vacuole- 

 like spaces approximately circular in section. The nuclei are well separated. 

 As a rule the number of blood corpuscles contained in the glomerular vessels 

 is quite small, far fewer than in the resting glomerulus. This we think 

 may be due to the expulsion of the blood from the capillary loops after 

 excision of the kidney, or to post-mortem laking of the corpuscles. The 

 latter may be produced by the diffusion of water from the capsule through 

 the walls of the capillary loops after the epithelial cells have died, and 

 before the fixative has had time to act upon them. This would account for 

 the very characteristic vacuolated appearance of the glomeruli already 

 alluded to. 



We were never able to keep the blood in a kidney that was excised at the 

 height of activity. At the instant of excision such a kidney is hard and 

 tense, and instantly becomes soft when the first ligature is tied round the 

 pedicle. This is even the case though the vein be first ligatured, and though 

 the kidney may have been separated from its surrounding tissues before the 

 diuretic was administered in order to give ample time for closure of the 



