PERCENTAGE OF WATER IN BRAIN AND CORD 89 
ranged, according to increasing brain weight, the observed per- 
centages of water. The corresponding weights for the relatively 
light and for the relatively heavy brains were also averaged. 
If it turned out that on the average the higher percentage of 
- water went with the light brain lot, and the lower percentage 
with the heavy brain lot, the determination was considered 
‘accordant.’ The opposite relation was designated as ‘reverse.’ 
As it seems probable that the myelin is the principal cause of 
the differences for which correction should be made, it is not 
advisable to introduce corrections for brains from rats less than 
20 days of age, since previous to that age myelination is quite 
incomplete. On looking at table 1, it will be found that begin- 
ning with the 20 day records there are observations for the 
percentage of water on a number of age groups, which com- 
prise five or more individuals. Of such groups we have used 38 
from the male, and 32 from the female records. Each of these 
groups has been treated as indicated in the sample table which 
follows. The details of this entire operation are here given. 
The data for each individual were arranged according to in- 
creasing body weight. After the body weight of each rat was 
entered the observed brain weight, and after this the brain 
weight to be expected for the body weight (not the age) was also 
entered, using table 68 (Donaldson 715) for the expected brain 
weight values. If the observed brain weight is found to be 
greater than that to be expected from the body weight then the 
brain is large, and vice-versa. 
Using the brain weight values taken from table 68 as the 
standards, the percentage value of each difference was deter- 
mined, and this was entered opposite the brain weight to which 
it applied. These percentage differences were next arranged in 
regular order from the most minus to the most plus, and of the 
series thus formed either the first third or first half Gn this in- 
stance the first three) of the cases was used for comparison with 
the ‘ast third or half. 
The three minus cases give an average deficiency in brain 
weight of 6.2 per cent and show 78.57 per cent of water ob- 
