CHANGES IN WEIGHT OF CENTRAL NERVOUS SYSTEM 665 
be satisfactorily explained, the formula which had been suggested 
for determining the weight of the central nervous system seemed 
to have only limited applicability. 
For this reason, in 1901-02, I endeavored to get data which 
would show whether a regularseasonal variation took place. Since 
that time, I have examined for the same purpose other series of 
frogs in 1908 and also in 1909. 
The general result of these observations is to show that the 
relative weight of the central nervous system of the leopard frog 
does change during the year, being constant during hibernation, 
low in the spring, high in the summer and low again in the 
autumn, when the frogs go into hibernation. 
The discussion which follows is intended to present 
I. The evidence that a seasonal change occurs. 
II. The biological interpretation of this change. 
I. THE EVIDENCE THAT A SEASONAL CHANGE OCCURS. 
TECHNIQUE AND SOURCES OF ERROR 
In all of the series about to be described, the technique for 
examination has been essentially uniform. Specimens of Rana 
pipiens, the leopard frog, alone were used. The frogs were kept 
moist for several hours before dissection. They were killed with 
chloroform and the body weight =(Bd. W.) taken to the nearest 
0.1 gm. The frog was next either suspended or laid flat on its 
ventral surface, with the legs fully extended, and the distance 
from the tip of the nose to the tip of the longest toe taken with 
a jointed calipers and then read off on a scale to the nearest mil- 
limeter =(total length). While in the ventral position, the 
long axis of the head was brought in line with that of the body 
by raising the head with a small wooden wedge, and with a vernier 
calipers the distance from the tip of the nose to the tip of the 
urostyle—the cartilaginous end of which was exposed by a slit 
through the skin—was measured and read to the nearest 0.1 
mm. =(body length). 
The frog was then placed on its back, opened and all the viscera 
removed. 
