DIFFERENTIATION AND REJUVENATION 153 



that excess of development of one function of the cell, 

 a modification in the structure is necessary. The ap- 

 paratus in the interior of a cell to produce the ex- 

 aggeration of the function must be developed, so that 



FIG. 57. AMCEBA PROTEUS, photograph of a specimen prepared by 

 Prof. G. N. Calkins. 



to effect the complex physiological machinery of the 

 adult body, this differentiation, of which I have so 

 often spoken, is indispensable. A nerve cell carries 

 on all the vital functions, but it has in addition a special 



