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C. G. MACARTHUR AND E. A. DOISY 



2 Substances in italics were determined in this investigation. 



average deviation. Not until many such series have been de- 

 veloped shall we be able to state what normal brain growth really 

 is. To a certain extent, a smooth curve averages the data, but 

 this may introduce larger errors than it attempts to average. 

 There is no way of knowing definitely that a curve should be 

 regular as given or made up of a series of waves of different sizes. 

 This also can be determined only by a larger number of 

 investigations. 



If the thirty-five-year-old brain is normal, there is a rather 

 wide range of variability. It will be noticed that the total 

 solids in this brain are 5 per cent higher than in the other adult 



