158 Viewpoints in the Study of Growth [Jan. 



this the energy aspects and speaking in terms of calories. Lastly 

 there are the considerations of the gross increase in size and form 

 and other features, in which Statistical factors assume the dominat- 

 ing importance. None of these aspects are without significance in 

 the conception of growth; and if the biology of its processes still 

 seems obscure, we must remember the complexity of the factors and 

 forces which interplay in life. 



What is growth? One cannot penetrate far into the literature 

 of the subject without meeting with a bewildering confusion in the 

 significance of the term. Various expressions, such as growth, 

 organic growth, development, and euplasia have been applied to the 

 same phenomena ; and the numerous attempts to define their mean- 

 ing and precise application have almost invariably ended in a failure 

 to meet criticisms which might be urged against each definition sub- 

 mitted. The most general definition of growth is " increase in 

 volume " or " increase in size " (Huxley) . It has been pointed out, 

 however, that increase in volume does not always serve as an index 

 of organic growth ; f or the increase may merely be due to swelling. 

 Sachs defined growth as an increase in volume accompanied by a 

 change in form. Little is gained by defining growth as the result 

 of a process of molecular intussusception (Huxley) or as due to 

 excess of assimilation over disassimilation (Verworn). No uni- 

 versally acceptable definition has been framed; nor is it likely that 

 one can consider all of the manifold features of growth in a single 

 category. Some of the more familiär uses of the word growth are 

 even more confusing than the so-called scientific definitions. Thus 

 it is Said that a tumor " grows," though the processes described may 

 be quite unlike the growth of an organism. And in the " growth " 

 of a hydrocephalus the analogy is stretched still further. What is 

 needed today is less of theory and more of facts upon which to 

 build a more substantial conception of growth and formulate its 

 fixed characteristics in words. 



The justification to dwell for a moment upon a review of the 

 more adequate definitions proposed lies in the emphasis which this 

 may throw upon some of the problems encompassed in the concept 

 of growth. Lee has presented the analysis of growth in these 

 words : " All growth, whether of the cells, the tissues, or the organs, 

 is the result of no more than three processes, viz., multiplication of 



