ANATOMY: H. H. DONALDSON 
353 
By way of introduction the following data from the literature are 
presented (de Regibus^*^). 
iiln man at birth the brain has about 88% of water and both the 
gray substance (in which cell bodies are abundant), and masses of 
fibers alone (later to become Vhite substance'), have the same per- 
centage. At maturity, however, the case is very different, as will be 
seen from Table 2. 
TABLE 2 
Percentage of water. Fluman brain 
CORTEX 
(gray) 
per cent 
At Birth 88.0 
At Maturity. 86.0 
According to this table the (gray) cortex has lost 2 points and the 
(white) callosum, 17.6 points in the process of maturing. 
It is never possible to obtain at maturity the cortex, or any other 
gray mass, without an admixture of some myelinated fibers, and I 
have therefore credited one point of the loss, noted in the water content 
of the cortex, to the presence of such fibers. 
According to this assumption the mature gray substance, when the 
myelin of the myelinated fibers is excluded, contains 87% of water. 
In the computations which follow, the neurons ( = cell bodies and 
axons), without myelin, are assumed to have 87% of water. 
The fact that the fibers without myelin (see Table 2) have at birth a 
high percentage of water (88%) while at maturity, after myelination, 
they have lost 17.6 points, indicates that either axons of this type have a 
peculiar capacity for losing water, or that the accumulation of myelin 
has caused the reduction observed. 
To obtain a notion of the approximate distribution of the water 
between the myelin and neurons proper, it is necessary to have data on 
the relative abundance of these two constituents of the brain. 
In 1913 W. Koch and M. L. Koch^^ made a study of the chemical 
composition of the brain of the albino rat at six ages, between birth and 
maturity, and of the spinal cord, at one age. The data thus obtained 
are those which will be utilized here. The authors determined seven 
fractions: — proteins, organic extractives and inorganic constituents, 
which three taken together, we shall designate, protein (or non-lipoid) ; 
and phosphatides, cerebrosides, sulphatides and cholesterol, which 
four taken together, we shall designate, Kpoid. 
These data give us at each age, therefore, the protein and the lipoid 
callosum 
(white) 
percent 
88.0 
70.4 
