CHANGES IN WEIGHT OF CENTRAL NERVOUS SYSTEM 685 
In this series it is to be noted that the heaviest frogs are prob- 
ably three years older than the lightest. At 22.7 gms., v. Bezold 
finds the percentage of water in the early summer to be 78.2, 
which is in good agreement with my July record of 78.7 (average 
of both sexes) for frogs the average body weight of which was 22.4 
ems. 
Since in table 10 the body weight values—save for April 
(females) and January (both sexes)—are nearly alike, the vari- 
ations in the percentage of water cannot well be explained as due 
to size. On the other hand if the frogs were from eggs of the 
same year, except in the instances above indicated, the specimens 
examined later in the season must be older than those taken ear- 
lier. Advancing age would demand a fall in the percentage of 
water and this fall as we have seen, occurs. But the fall in turn 
gives way to arise in the percentage of water after the beginning 
of September. To explain this latter result, I can merely suggest 
that it occurs as active feeding comes to an end and when the frog 
is less well supplied with food than in the early part of the summer, 
and thus it may represent a condition of underfeeding or starva- 
tion which has been shown by Moraczewski. (00) to cause the 
percentage of water in the entire frog to rise.’ 
It is evident therefore that age and food conditions at least have 
an influence on the percentage of water in the entire frog, but the 
results, like those given in table 10, cannot be fully explained until 
it is determined first whether there are additional important con- 
ditions, and second, how these conditions which we do recognize 
interact. 
Before leaving this topic it is important to state that in both the 
brain and the spinal cord no systematic variation in the percent- 
age of water can be observed during the active season. This 
statement is true for all three lots of frogs. Moreover, as shown 
in table 12, the averages for the percentages of water in the brain 
and cord (using the data in tables 3, 4 and 6) are nearly alike for 
all three lots of frogs. 
2 In the paper cited above, Moraczewski’s general conclusion 2, page 144, is con- 
tradictory to his tables. The above statement in the text is based on the tables 
and on the text on page 136 of the paper cited. 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 3 
