l82 PAUL WEISS 



compared systems resemble each other closely enough in their mode of 

 growth to be essentially commensurable, or to the existence of some un- 

 defined principle of organismic nature, exercising overall control over 

 the multiplicity of heterogeneous components involved in growth, can 

 only be decided after a detailed analysis of the underlying phenomena. 

 At any rate, a purely formal treatment of growth, as is often attempted 

 through the interpretation of growth curves, is only a valuable guide to 

 and supplement of, but never a substitute for, a precise analysis of the 

 different forms in which growth manifests itself. 



There can be no research on growth as such. We can only study grow- 

 ing objects. And different growing objects follow different methods. 

 The growth of a differentiating metazoan introduces aspects not pre- 

 sented by the growth of a bacterial culture, and the growth of a higher 

 plant has still other peculiarities. As we have pointed out repeatedly, 

 each individual tissue and organ has its peculiar mode of growth. To 

 know growth we must therefore first break down each one of its mani- 

 festations into its constituent elementary processes and then study these 

 and describe them in objective terms. This is a long way to go, but 

 there is no short cut. 



In our present primitive stage of knowledge impatient attempts to 

 formulate a general and universal theory of growth seem to have little 

 chance of success. Those general theories that are sporadically being ad- 

 vanced are usually "general" only in the sense that they are first derived 

 from some rather special segment of the growth problem and then 

 broadly generalized by proclamation or mere implication. Consequently 

 they may be sound and pertinent within the area of their derivation but 

 gratuitous and invalid in their illegitimate extensions. Oversimplification 

 of facts and overgeneralization in theory are the main causes of the 

 existing discordance among the several contending concepts of growth. 

 Unless we desist from those practices the confusion is bound to grow, in 

 spite of all the excellent experimental work being done in various areas. 



Growth is not a simple and unitary phenomenon. Growth is a word, 

 a term, a notion, covering a variety of diverse and complex phenomena. 

 It is not even a scientific term with defined and constant meaning, but a 

 popular label that varies with the accidental traditions, predilections, and 

 purposes of the individual or school using it. It has come to connote all 

 and any of these: reproduction, increase in dimensions, linear increase, 

 gain in weight, gain in organic mass, cell multiplication, mitosis, cell 

 migration, protein synthesis, and perhaps more. It is gravely inconsist- 

 ent to apply the most exacting standards of precision to our research 



