PERCENTAGE OF WATER 141 



and gray mixed); (4) cerebellum; (5) pons; (6) medulla oblon- 

 gata. 



For the percentage of water in the human encephalon at birth, 

 the determinations for these several localities are averages from 

 three male and five female newborn infants. 



A series of tes+s applied by me to Weisbach's data for mature 

 brains have shown that the percentage of water in the entire 

 encephalon is approximately equal to the sum of four times that 

 in the white substance (1) ; five times that in the gray substance 

 (striatum) (2); and once that in the cerebellum (3) divided by 10. 



This procedure gives for the percentage of water in the human 

 brain at birth 88.34 per cent. The value thus obtained is probably 

 nearly correct. 



By the same procedure I obtained from Weisbach's data for 

 children between three and fourteen years of age (2 males: 3 

 years and 8 years; 2 females: 4 years and 14 years) a mean value 

 for the entire encephalon of 79 . 2 per cent at 9.5 years. Finally, 

 Weisbach's records for 64 males and 17 females, 20-30 years of 

 age, give a mean value of 77.0 per cent. 



Turning now to the determinations of Koch ('09) we find his 

 average determination of the percentage of water in five human 

 encephala at maturity to be 77.8 per cent. In a female brain 

 of two years, he gives the percentage of water in the cortex of 

 hemispheres as 84.49 per cent and in the callosum as 76.45 per cent. 



In a male of 19 years, the cortex was found to have 83.17 per 

 cent and the callosum 69.67 per cent. This last case may be taken 

 to represent the conditions at maturity. This being assumed, 

 it was found that combining the determination for the cortex 

 in the proportion of 603 times to 397 times of that for the white 

 substance gave a mean percentage of 77.8, which is Koch's deter- 

 mination for the water in the entire encephalon at maturity. 4 



Using the same proportions as those just given for the gray 

 and white substances at maturity and applying them to the data 

 for the brain at two years, mentioned above, we obtain as a mean 



4 The proportional abundance of the gray and white substance in the encephalon 

 is not to be inferred from the numbers given above. Each investigator has used 

 more or less arbitrary criteria for the gray substance, and a treatment of the 

 results of an author in the manner here followed, has a value for the determina- 

 tions by that author alone. 



