BASIS OF INVESTIGATION. 77 



extreme functional activity carried on through a considerable period 

 of time. If, after acquiring physical development through special 

 training, he desists from further exercise, his strength and activity 

 will drop away rapidly and to a considerable extent. Then we would 

 have a case of use followed by disuse. The amount in which 

 strength will fall away by disuse will depend upon the length of 

 time during which training was continued. If training be con- 

 tinued for only a short time, then strength would fall away rapidly, 

 while if continued a long time it would fall away less rapidly and 

 to a less extent. 



GROWTH OF THE BRAIN. 



The growth and development of the brain are similar to those 

 of the IxDdy, but are continued for a much longer time. The brain 

 differs from the body in that its functional capacity may be enor- 

 mously increased without apparent increase in its size. For what 

 length of time the brain continues to grow in size is uncertain, but 

 it appears that the time is extended and the brain is made more 

 capacious by intellectual activity. In Fig. 2 I give Galton's dia- 

 gram of brain growth as determined by him from students at the 

 University of Cambridge, England. The original diagram is lim- 

 ited to twenty-five years of age, but I have extended it by dotted 

 lines to thirty-three, to illustrate the probable growth to that period. 

 From personal observation I find that in spite of my hair growing 

 thin I wear a slightly larger hat than I found necessary at the age of 

 thirty. From this it would appear that either hats have grown 

 smaller or the growth of the brain continues beyond thirty. The 

 functional capacity, however, continues to increase long after the 

 limit of size is attained. Time is, therefore, an important element 

 in brain development, and it becomes evident that there can be 



