PERCENTAGE OF WATER IN BRAIN .AND CORD 87 
per cent so that a difference of 1 mgm. of brain in this group 
corresponds to a difference of 0.0012 in the percentage of water. 
Factors for correcting the percentage of water according to 
brain weight 
The result of treating the data in this manner was to show 
that of 38 male groups 64 per cent, and of 32 female groups 66 
per cent were accordant. In the case of each age group further 
calculations were made. Taking as the standard the average 
of all the tabular brain weight values entered, the absolute dif- 
ference between the average weights of the light and the heavy 
brains was computed and expressed in milligrams. The differ- 
ence between the mean percentage of water for the light and 
for the heavy groups was also found. Then, by dividing this 
difference in the percentage of water by the difference in weight, 
expressed in milligrams, the difference for 1 mgm. was found. 
The number thus found I designate the ‘correction factor.’ 
The preceding paragraphs give an example of the foregoing 
procedure. 
Of course, such a factor was obtained for each age group in 
each sex and was found to be accordant, as stated, in 64 per 
cent of the male, and 66 per cent female groups, but reverse in 
the remaining groups. In the case of each sex the sum of the 
reverse factors was deducted from the sum of the accordant 
factors and the remainder divided by the number of accordant 
cases. This gave the correction factor for each sex. 
The results are as follows: 
Correction Factors 
Male brain: 0.0013 per cent water for a difference of 0.001 gram 
Female brain: 0.0012 per cent water for a difference of 0.001 gram 
The correction factor selected for both sexes was 0.0013 and 
this has been used in correcting the observed percentages of 
water as given in table 1. 
The object of this treatment of the crude data was to reduce 
the deviations in the percentage of water which depended on 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 1 
