IV 



DIFFERENTIATION AND REJUVENATION 



J^ADIES AND GENTLEMEN: In order to 

 present the subject of this evening, I will take a 

 few brief moments at the beginning to review the 

 results reached in the previous lecture. I spoke then 

 of the phenomena of growth and endeavoured to make 

 clear to you what I consider the fundamental con- 

 ception of this study that the decline in the growth 

 power is extremely rapid at first and slow afterwards. 

 This change in the rate of growth is of course due to 

 things in the animal body itself. It is a logical con- 

 clusion for us to draw that if we are to study out the 

 cause of the loss of growth power, we should do it 

 rather at that period of development when the change 

 in the rate of growth is most rapid, for then we should 

 expect those modifications to exhibit themselves most 

 clearly because the magnitude of cause is likely to be 

 proportionate to the magnitude of result, or, in other 

 words, when the decline is most rapid, then we must 

 expect to find the alterations which cause that decline 

 in the organism to show themselves most conspicu- 

 ously. You will remember, further, that we spoke of 

 growing old as being a much more complicated ques 



