376 
KUTH B. ROWLAND 
with 2.037 sq. mm. in the compensating organ — an increase of 
more than 100 per cent (table 1). 
A comparison of the volumes of the cells making up the walls 
of the two kidneys is likewise of great importance in determining 
the nature of the response brought about by a unilateral opera- 
tion. Although in the calculation of the surface area of the 
tubules it seemed sufficiently accurate to regard them as cylin- 
ders with the average circumference as their boundary, it did not 
seem possible to apply such a geometrical method in estimating 
the volume of the walls, for the cells (figs. 11 and 12), especially 
in the normal kidney, often bulge out into the lumen, making 
this, as seen in projected outline, very irregular. The method 
already described in the selection of a normal model was again 
TABLE 1 
Showing the area of the inner or secreting surfaces of the normal kidney, P.V 7 d, 
and the hypertrophied kidney, PN 7 
SERIES NUMBER 
PN 7 d (normal) 
PN 7 (hypertrophied) . 
INNER 
CIRCUMFER- 
ENCE 
(X 600) 
OUTER 
CIRCUMFER- 
ENCE 
(X 600) 
LENGTH 
(X 600) 
AREA OF 
INNER 
SURFACE 
(X 360,000) 
cm. 
7.8 
13 
cm. 
13.6 
18.6 
cm. 
465 
564 
.sg. cm. 
3627 
7332 
ACTUAL 
AREA OF 
SURFACE 
1.007 
2.037 
used (p. 373). Paper of uniform weight was obtained, and to 
insure further accuracy, section number one of the normal 
kidney was projected on one half of a sheet, section one of the 
hypertrophied organ on the same sheet of paper, and so on 
through the series. The walls of the two kidneys were then cut 
out, and the aggregate of each weighed separately. The paper 
representing the walls of PN 7 d weighed 20.39 grams that of 
PN 7, 33.4 grams, showing an increase of 63 per cent in the 
weight of the latter. Since the weight in this case is in direct 
proportion to the volume, the hypertrophied kidney may then 
be considered as showing an increase of almost two-thirds beyond 
the normal. A count of the nuclei in each kidney, all the sec- 
tions of which were cut at lO^t, shows a small percentage (16 per 
cent) of increase in the number of cells found in the larger kidney, 
