314 DAVID H. DOLLEY 
the-knife,”’ but in view of the explanation made and the results 
to be shown, this is negligible. 
Twenty cells were measured to a stage. ‘There were thus 200 
cells (10 stages) measured from the control and 220 (11 stages) 
from the exercised animal. Stage 11 was not measured in the 
control for the simple reason that none was found. 
The procedure was to outline the accepted cells one after 
another by means of the camera lucida (Zeiss). The lens system 
used was the Zeiss comps. oc. 12, homo. 2 mm. oil immersion, 
tube length 153 mm., X 1960.at stage level. The magnifica- 
tion was adjusted to conform to some previous measurements, 
and it is believed that the area determined from larger magnifi- 
cations is less subject to small mechanical errors. At the point 
where the dendrite becomes of uniform size the cell outline was 
closed. When the full set was outlined, the area in square cen- 
timeters was read for each cell from the polar planimeter.. At 
the same time, the maximum longitudinal and transverse di- 
ameters of cell and nucleus were measured in one-half millimeters, 
to compare and test the accuracy of this previous method. The 
areas and dimensions were then averaged for each stage set. 
The average diameters are set forth in table 2 and the average 
areas in table 3 under that head. 
From the average diameters the average relative volumes of 
cells and nuclei were estimated. The third dimension being un- 
known, it can only be approximated on the basis that it will 
average the same as the transverse diameter—another thing 
that individual cell reconstructions bears out. The term rela- 
tive volume is used because the volume was calculated as that 
of a parallelopiped, namely, the length by width by depth—the 
longitudinal axis multiplied by the square of the transverse. 
Mathematically, the formula for such elliptical bodies is 3 [2a.- 
x. (b)2], in which a and b represent the major and minor radii. 
For the sphere it becomes % (7 r°). 
If the ratio between two such bodies whose radii are a and b 
and a’ and b’ respectively be expressed as a fraction, it becomes 
; a b? 
on cancelling out the common factors ——, or the diameters 
a 
b’?’ 
