Relation of Cortex to Volume. 527 
and hj. This leaves the curve entirely out of account. If we 
add to this mean the greater area multiplied by kl and then di¬ 
vide this by 2 we have an area which is represented by the 
line mn and which is as near as we can get at the truth not 
knowing the exact curve. In this manner the volume of each 
kidney was calculated, and by subtracting the volume of the 
medulla the volume of the cortex was obtained. 
The kidneys were then taken and with a sharp scalpel the 
cortex and medulla were separated as accurately as possible. 
The volume of each was then found by displacement and used as 
a control for the figures obtained. 
The results are given in four tables. The thickness of the 
medullary portion in the two end sections is not the thickness 
of the section because the thickness of the cortex must be sub¬ 
tracted. The volume is first found by multiplying one-half of 
the sum of the two areas of any section by the thickness of 
section. This is given in column A. The volume found by 
multiplying the greater area by the thickness is given in column 
B. The volume of the medulla is found in the same way, with 
the exception of the two end sections where the thickness of the 
medullary portion is less than that of the section. The mean 
is given at the foot of the column. This should be compared 
with the results found by displacement. The aggregate volume 
of the four kidneys, the volume of which was computed, was by 
displacement in water 53.5 cc., while by the method of computa- 
tation it was 53.23 cc. This shows that while in the computa¬ 
tion of a single kidney there is a slight error, it is so small it 
may practically be disregarded. The aggregate volume of the 
medulla in the four kidneys was 14.5 cc. by displacement and 
14.00 cc. by computation. The area in the the tables is ex¬ 
pressed in square decimeters. The average per cent, of cor¬ 
tex by displacement in the four pair of kidneys used fresh was 
Cat 1. Cat 2. Cat 3. Cat 4. 
.645 .667 .719 .729 
The average for four pairs is . 690. The per cent, of cor¬ 
tex, by volume, shown by computing volume of medulla and 
entire volume is 
Cat 1. Cat 2. Cat 3. Cat 4. 
.575 . 679 .766 . 784 
