ANATOMY: H. H. DONALDSON 
351 
content of the central nervous system have been followed as a phenome- 
non of growth (Donaldson^' ^> 
The progressive loss in the percentage of water in the brain and in 
the spinal cord is closely linked with age, although it can be slightly 
modified by nutritive conditions. The age of the animal becomes 
therefore the most important datum when a determination of the per- 
centage of water is to be made. 
In Chart 1 the change, on age, of the percentage of water in the brain 
and in the spinal cord of the male albino rat is shown by graphs. The 
observed mean values for groups of cases are indicated by small dots, 
for the brain, and by small triangles, for the cord. The respective 
graphs were determined by formulas devised by Dr. S. Hatai, and based 
on the observed group values (Donaldson^). Along the graph for the 
brain are seen four large dots. These represent observations on the 
human brain — taken from Koch and Mann, and from Weisbach.'* ^ 
Table 1 gives the percentage of water and the age of the human brains 
here used and also the equivalent rat ages. 
AliJJIXO 11 AT 
0 25 50 100 150 200 250 300 350 
DAYS 
ea 
66 % CHART 1 
Showing the percentage of water, on age, in the central nervous system of the albino rat. 
The upper graph gives the values for the water in the brain as determined by the formulas 
(Hatai — in 'The Rat,' Donaldson,^ — 1915). The lower graph gives the corresponding 
values for the spinal cord, determined in t^e same way. 
The small black dots indicate the observed values for the several age groups for the 
brain — and form the data for the formulas. The small black triangles have a like value 
in relation to the spinal cord. 
The large black dots along the graph for the brain represent the human data as given in 
Table 1. 
