1/4 Viewpoints in the Study of Growth [Jan. 



and nervous System, only in the embryonic period; others again, 

 like the glands, diiring a variable period after birth. So long as so 

 much emphasis is placed upon the cell in growth we deserve to know 

 more about its morphological history in this crucial period ; and this 

 applies above all to those tissues, the so-called ductless glands, like 

 the hypophysis and thymus which it is currently customary to asso- 

 ciate in some way with growth. Until very recently the interest of 

 histologists has centered either in the embryonic or the adult tissues 

 of mammals, with scanty consideration of the intervening stages. 



The importance of a comprehensive consideration of nutrition 

 in growth need not be dwelt upon in detail. The conflicting views 

 which have been held since Liebig's time regarding the significance 

 of protein in nutrition have had their counterpart in the explanation 

 of growth. Voit assumed that the protein metabolism of the grow- 

 ing organism is unlike that of the adult. The inadequacy of the 

 theories which associate growth with a decreased power of protein 

 katabolism no longer requires emphasis. Now that we know of the 

 marked chemical and biological differences existing between pro- 

 teins from different sources the significance of these facts in nutri- 

 tion must be further established. 



Important economic considerations are involved in the ability 

 to modify growth or accomplish it at lessened expense, — a possi- 

 bility for which nutritive factors offer the only probable oppor- 

 tunity at present. Hence arises the practical importance of some 

 of the Problems in this field. Broadly put, one problem reads : How 

 can inefficient native f oods be made efficient, and what is the relative 

 economy of different dietaries and adjuvants ? 



The questions which arise in connection with the duration of 

 the capacity to grow have already been alluded to. Will growth, 

 suppressed by the necessary restrictions in diet, cease entirely for 

 an indefinite length of time ? What happens to an animal suffering 

 such a Suspension of growth, when it is given an abundant diet? 

 What are the tissue changes accompanying these suppressions and 

 realimentations, i. e., what are the attendant histological features? 



The function of age is evidently an important matter for con- 

 sideration in questions of growth. An index of age apart from 

 the record of birth is much to be desired. Weight and size in gen- 

 eral may be inadequate for many obvious reasons. What can be 



