Relation of Cortex to Volume. 
537 
injected with the gelatin by a constant pressure apparatus. 
They were hardened in 95 per cent, alcohol. Three portions of 
cortex were then cut from the cortex in three different loca¬ 
tions. One on the surface, one near the boundary line of 
cortex and medulla and one through the entire cortex. These 
were stained in toto and imbedded in paraffin. Serial sec¬ 
tions were cut .10 mm. in thickness as this was found to be 
about the average diameter of the glomeruli in a former series 
of measurements (.1027 mm. exact). A glomerulus could not 
appear in over two sections and possibly in only one. The out¬ 
line of each section was traced on paper with a camera lucida 
and a dot made on the paper wherever a glomerulus was seen. 
The area was found with a planimeter. The sum of the areas 
of the sections multiplied by the thickness gave the volume ex¬ 
amined. Some glomeruli appeared in two sections and it was 
necessary to find what per cent, did so. This was accomplished 
* by tracing two consecutive sections on paper — the under sur¬ 
face of one and the upper of another — and finding which 
glomeruli coincided. The sections w T ere also carefully exam 
ined microscopically. On examining several sections in this 
manner, it was found that from one-half to 83 per cent, of the 
number of glomeruli in any section represented the actual num¬ 
ber of glomeruli present. The volume of block I was calculated 
to be .31160 cc. The sum of the glomeruli in each section was 
634, but according to the above calculation it would contain 
from 317 to 529 glomeruli. The average volume of the cat’s 
kidney was found to be 12.9 cc. for both right and left kidneys. 
The cortex was found to be .7 of the entire volume of the kidney. 
For an average-sized kidney this would be 9.03 cc. 
9.03 cc. -r- .31160 cc. = 28.97. 
317 X 28.97 = 9183.49 glomeruli. 
529 x 28.97 = 15325.13 glomeruli. 
According to block I the number of glomeruli would vary be¬ 
tween the two figures just given. 
The volume of block II was found to be .2565 cc. The sum 
of the glomeruli was 723. The exact number would be between 
362 and 603. 
9.03 cc. -r- .2565 cc. = 35.20. 
362 X 35.20 = 12742 glomeruli. 
603 X 35.20 = 21226 glomeruli. 
