CHANGES IN WEIGHT OF CENTRAL NERVOUS SYSTEM 669 
jars in the laboratory until examined. Enough frogs were taken 
to give as a rule four of each sex, and the endeavor was made to 
have them of nearly the same size, 7.e., 22-29 gms. in body weight. 
A glance at table 2 will show that this effort was largely success- 
ful. The measurements which were made included (1) the total 
length, (2) the body weight (3) the weight of the brain (4) the 
weight of the spinal cord, as well as the length of each of these 
portions of the central nervous system and the percentage of water 
in each. 
These data, from 1-4, are necessary for determining the value 
of the constant C in the formula 
Weight of C. N.S. = (Log Wx yL)C. 
It will be seen from the inspection of the formula that if there 
are two frogs of the same body weight and the same total length, 
but differing in the weights of their central nervous systems, then 
in the case of the frog with the lighter nervous system, the value 
of C will be less than in the other, for by the terms of the formula, 
the weight of the central nervous system is 
C times (Log Wx \L) 
a value which in this instance is the same for both the frogs. 
It becomes therefore possible to express the changes in the rela- 
tive weight of the central nervous system by the differences in 
the value of C—and it is this method which has been here em- 
ployed. 
This variation in the constant C not only enables us to express 
the variations in the relative weight of the central nervous system, 
but is by far the best method available for the purpose, as it is 
quite independent of the absolute size of the frog in any instance. 
In table 1, the average value of C is given together with the 
range in this value for each series. 
If these average values for successive weeks are plotted, they 
show great irregularity. By grouping the series however, so as 
to take the first one alone, then the next three series as the second 
group, and finally the remaining series up to the very last one in 
groups of four, and the last one again alone, we obtained the data 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 3 
