ON THE PERCENTAGE OF WATER IN THE BRAIN 

 AND IN THE SPINAL CORD OF THE ALBINO RAT 



HENRY H. DONALDSON 



The Wistar Institute of Anatomy and Biology 



WITH FIVE FIGURES 



The object of this study has been to obtain a continuous record 

 of the change in the percentage of water in the central nervous 

 system of the albino rat during its life cycle, and to correlate this 

 with the other important changes in the nervous system which 

 are commonly recognized. These results in turn should put us 

 in a position to determine to what extent and in what way this 

 character may be modified. 



Although it has long been known that at birth the percentage 

 of water in the central nervous system was much greater than at 

 maturity, yet the change in this character through the life cycle has 

 never been systematically followed, and it thus happens that there 

 are no other extensive records with which to make comparison. 

 The relations of existing data to this investigation will be discus- 

 sed later on. 



The data used for the following study were largely obtained 

 from the same animals which furnished the records employed for 

 the two previous researches on the weight of the brain and of the 

 spinal cord of the albino rat under different conditions of age, 

 body-weight and body-length (Donaldson '08 and '09) although 

 many cases have been necessarily excluded because the percentage 

 of water had not been determined. On the other hand, a few new 

 records have been added to the original series. 



In carrying on this work, which has extended through a number 

 of years, I have been greatly assisted by Dr. Hatai, as well as by 

 two of my former students, Dr. Polkey and Dr. Whitelaw, both of 

 whom made a number of the determinations of water under my 



