236 AGE, GROWTH, AND DEATH 



Weismann has gone much farther in the elaboration 

 of the conception of life units than any of the other 

 writers. He thinks the smallest of the life units are 

 biophores. A group of biophores brought together 

 constitutes another order of life units which he calls 

 determinants; the determinants are again grouped and 

 form ids ; and the ids are again grouped and form 

 idants. If you want to accept any theory of life units, 

 I advise you to accept that of Weismann, for it offers 

 a large range for the imagination, and has a much 

 more formidable number of terms than any other. 



I want to pass now to an utterly different line of 

 study, the question of psychological development. If 

 it be true that the development is most rapid at first, 

 slower later, we should expect to find proof of that 

 rate in the progress of mental development. In other 

 words, we should expect to find that the baby de- 

 veloped faster than the child mentally, that the child 

 developed faster than the young man, and the young 

 man faster than the old. And do you not all instinc- 

 tively feel immediately that the general assertion is 

 true? In order, however, that you may more fully 

 appreciate what I believe to be the fact of mental 

 development going on with diminishing rapidity, I 

 should like to picture to you briefly some of the 

 things which the child achieves during the first year 

 of its life. 1 When the child is born, it is undoubtedly 



i I am indebted to Dr. Benjamin Rand of Harvard University for guidance 

 to the literature upon the subject of the mental development of children. The 

 account in the text is the result of reworking the recorded data, so as to 

 elucidate the relation of the child's mental progress to its age, none of the 



