122 HENRY H. DONALDSON 



rapid at the time when the brain is growing most actively. Table 

 1 further shows that the percentages for the females are in general 

 slightly less than those for the males of the same body weights. 

 Chart 1, which is based on table 1, exhibits this relation. 



As we shall see later, the percentage of water in the central 

 nervous system is more closely correlated with age than with the 

 body weight or brain weight. Nevertheless, it will most often 

 occur that it is desired to estimate the probable percentage of 

 water in cases where the weight of the body or brain alone are 

 known, and the foregoing table 1 furnishes the means of doing 

 this for animals which have been grown under the ordinary normal 

 conditions. 



It has been already demonstrated (Donaldson '06) that for a 

 given age, the body weight of the female is less than that of the 

 male, consequently the comparison in each case is here between 

 males that are younger than the females with which they are con- 

 trasted, and as increasing age is an important factor tending to 

 reduce the percentage of water, it follows that the males, which 

 are younger, should show, as they do, a slightly greater percentage 

 of water. 



Percentage of water in the spinal cord. In the spinal cord the 

 relative loss of water with increasing body weight is greater than 

 in the brain, being from 15 to 16 units. Although the initial per- 

 centage is somewhat less, yet the subsequent loss is regularly more 

 rapid than that in the brain. The percentage of water in the two 

 sexes is related in the same way as in the brain. The observations 

 are given in table 1 and in chart 1. 



Percentage of water in relation to age. To support the sugges- 

 tion that the males in the foregoing tables show a greater per- 

 centage of water, because they are younger than the females, the 

 data have been rearranged according to age. In many cases the 

 age was not known, and this reduces the number of records to 358 

 males and 169 females. The results in the form of mean values, 

 based on a correlation table are given in table 2 and plotted in 

 chart 2, the entries being made for ten day intervals. When thus 

 arranged, it appears that in the brains of males and females of 

 like age, the percentage of water is similar. 



