PERCENTAGE OF WATER 125 



of the spinal cord which for a given age is relatively somewhat 

 greater in the male than in the female (Donaldson, '09 pp. 163- 

 164). The effect of this lengthening would be to diminish the 

 percentage of water. The influence of passive lengthening is dis- 

 cussed more fully later on. 



Theoretic curves. When we take the more extensive series of 

 mean values which is that for the males as given in table 1, and 

 draw the theoretic curves based on them, we obtain the rela- 

 tions shown in chart 3, the entries being arranged according to 

 body weight. The data for this chart are given in table 3. For 

 the formulas for these curves, I am indebted to Dr. Hatai. 



The formulas for the percentage of water in the brain of the 

 male albino rat are as follows: 



Up to a body weight of 30 grams 



y = 99.5 - - 12.6 log (x + 3.5) [1] 



and from a body weight of 30 grams on 



y = 82.62 — 2 log (x - 10) [2] 



In the case of the percentage of water in the spinal cord of the 

 male albino rat we have for body weights up to 35 grams 



y = 94.9 — 12.8 log (x) [3] 



and from a body weight of 35 grams on 



y = 85.2 — 6.5 log (x) [4] 



In all these formulas y = the percentage of water and x = the 

 weight of the body in grams. 



The formulas are of the same type as those used to express the 

 growth changes described in several previous investigations 

 (Donaldson '08, '09; Hatai '09), and have their main value as 

 convenient expressions of the several series of observations. 



Calculations (based on table 1, down to and including the 

 entries for 275 grams body weight) show that in general for 

 given body weight, the females which are under these conditions 

 relatively older as compared with the males, have a percentage 

 of water lower by 0.37 per cent in the brain and 0.60 per cent in 

 the spinal cord. The theoretic values for the female can there- 

 fore be obtained approximately by applying these corrections to 

 the determinations here given for the males. 



Having thus presented the data on the percentage of water 



