164 THE GROWTH OK THE HRAIN. 



TABLE 36. SHOWING THE NUMBER OF DEVELOPED CELLS IN 

 THE CERVICAL ENLARGEMENT OF MAN AT DIFFERENT 

 AGES. (Kaiser.) 



Thus he is able to show that in this locality the 

 developed cells increase in number from the fifth month 

 of fcetal life to maturity, the number doubling between 

 the fifth and ninth months of fcetal life, and again 

 between birth and the completion of growth. The first 

 period of increase probably centres about the sixth 

 month of foetal life, during which time the absolute 

 increase in the central system is large, and the second 

 period in all probability occurs during the first seven 

 years of childhood, since by the end of that time the 

 central system has attained nearly its full weight. The 

 difference in the number of cells observed in the foetus 

 of thirty-two weeks and in the new-born child is pro- 

 bably not a mere error of observation, but indicates a 

 more rapid development of the nerve cells in the former 

 case, yet at the same time it has little significance for 

 the absolute number which will ultimately be developed, 

 because even the higher figure is only a trifle more than 

 one-half that representing the total number of nerve cells 

 in the adult. To determine the number of cells usually 

 functional at maturity, the observations on grown per- 

 sons must be many times repeated. There is also no 

 direct indication of the age at which the development 

 of the nerve cells in man ceases, yet if the changes in the 



