i6o Viewpoints in the Study of Growth [Jan. 



lation featiire in respect to composition and form, the time relations, 

 the anomalies and irregiilarities involved, are thus brought out. 

 Here, as elsewhere in physiology, abnormalities have often given 

 the clue to the iinderstanding of normal processes. 



Inasmuch as growth involves a more or less continuous change, 

 there is need of some criterion thereof — some suitable method of 

 ascertaining and measuring it. This is by no means as readily ac- 

 comphshed as might appear at first glance. Changes in body weight 

 are not always reliable guides. There are increments of weight 

 which are transitory and those which are permanent. Uncorrelated 

 increments of mass may occur in the body long after the conclusion 

 of what is properly termed the period of growth. A gain of weight 

 at the middle life, for example, may be due to a deposition of re- 

 serve materials. Increase in stature and certain other dimensions 

 are not without significance as indications of growth; for they allow 

 US to estimate the correlation between weight and size. Without 

 suitable proportionality of form perfect growth, to say the least, 

 cannot go on. 



How illusory the dependence on any one criterion of growth, 

 such as body weight, may be is illustrated by the interesting studies 

 of Waters and of Aron. These investigators have described condi- 

 tions of adverse nutrition in young animals in which no change '^in 

 body weight occurred during long periods of time. Nevertheless 

 the animals " grew " f rom the Standpoint of changes in stature and 

 body proportions. In some cases the skeleton grew at the expense 

 of other parts of the body, especially the flesh. Many of the organs 

 retain their weight under such conditions, while the brain grows to 

 reach its normal size. 



Is the constancy of live weight an indication of lack of growth? 

 If one allows the term "growth" for the phenomena of distor- 

 tionate change here cited, it must be admitted with Aron that the 

 " growth " depends principally on the tendency to grow possessed 

 by the skeleton. Evidently, then, there are limitations to the de- 

 pendence on weight measurements. They teil us nothing about the 

 intricate changes in the tissues that may distinguish the adolescent 

 from the adult form, nor do they serve as an index to the desired 

 development of the body in three dimensions, — in other words of 

 proportionate growth. Nevertheless the study of growth by weigh- 



