1/2 Viewpoints in the Study of Growth [Jan. 



ing and adult organisms; whereas, as is well known, others like 

 zein and gelatin by theniselves do not even suffice for this function. 

 The need of an adeqiiate siipply of energy in some form or other, 

 and of appropriate salts for tissue construction is obvious. The 

 importance of the latter gains an unsuspected proniinence when 

 one plans experiments with isolated food substances; for with the 

 ordinary natural food mixtures a reasonable modicum is already 

 provided. We are convinced from an extensive experience that 

 many failures to promote growth in experiments on artificial nutri- 

 tion have centered in the inorganic food ingredient of the selected 

 dietaries. In some instances the deficiencies, if such there are, may 

 involve some minute proportion of hitherto supposedly inessential 

 Clements like iodine, manganese, etc. The time and opportunity 

 for investigation along the lines here suggested has arrived. There 

 is, further, a considerable body of evidence to suggest that "hor- 

 mones " or " vitamines " or comparable stimulants of growth are 

 essential. It is f utile as yet to discuss their mode of action. In 

 any event, however, their röle among the external causes of growth 

 need not be that of a simple nutrient in the sense of yielding energy 

 or material for development. 



The analysis of growth into a controllable nutrition factor and 

 an inherent growth impulse has its significance for the appreciation 

 of the pathology of growth and the management of the situations 

 created thereby. It becomes clear that abnormal growth cannot 

 always be corrected by regulation of the external factors of diet, 

 etc. A limit to dietotherapy or other therapeutic measures is 

 ofttimes set by the inalterable inheritance of an imperfect Constitu- 

 tion, the basis of an adequate capacity to grow. 



To attempt to f ormulate " laws " from data which are not over- 

 abundant and which involve a considerable number of variables 

 can scarcely be expected to yield generalizations of a very exact 

 nature. Nevertheless there have been essays at probable laws for 

 growth. As an Illustration I may cite Lusk's generalization that 

 " during the normal development of the young of the same age and 

 species, a definite percentage of the food is retained for growth 

 irrespective of the size of the individual." Rubner has independ- 

 ently applied a quite similar law to the growth of all species except 

 man, as an expression of the belief that it requires the same energy 



