Chapter 2 



PRINCIPLES AND THEORY OF GROWTH 



Ludwig von Bertalanffy 



I . INTRODUCTION 



[a) Definition of growth 



The term, Growth, denotes those changes of a Hving system that are manifest as 

 measurable changes, and particularly as an increase in size. It is, however, obvious 

 that such definition needs qualification. Increase of body weight, for example, 

 by mere intake of water or deposition of fat is not considered as growth. A better 

 delimitation is reached if growth is connected with a basic characteristic of living 

 systems, namely, metabolism. Every living system maintains itself in a continuous 

 exchange, anabolism and catabolism of its components. Hence we may define: 

 Growth is the quantitative increase of a living system which results from the 

 prevalence of anabolism of building materials over catabolism. 



Building 7naterials of the organism are defined as components which — in contra- 

 distinction to low-molecular compounds like water, sugar, etc. — not only pass 

 the living organism but are produced in anabolic processes as complicated 

 compounds specific to the organism in question. These, in turn, give rise to a 

 wealth of biological structures above the chemical level. Hence growth is the 

 increase in size of living systems which results from assimilation, i.e. production 

 of materials which are specific for the living system in question, and are produced 

 by multiplication of already existing protoplasm. 



In this sense, growth of a living system, being a quantitative increase, is 

 distinguished from difi[ere7itiation, that is, increase in organization and heterogeneity 

 within a living system. 



Although these definitions are clear in the abstract, their implementation in 

 the concrete case is by no means unequivocal. This is the reason why there is 

 considerable argument regarding the definition of growth [e.g. Weiss, 1949, 1955a; 

 Linzbach, 1955). 



Assimilation is the transformation of non-living nutritive materials into living 

 protoplasm and its derivatives. This is essentially meant by the term, "building 

 material" of a living system. In this sense, growth may be defined (Rossle, 1923) 

 as "increase of structurally and functionally complete biomass" (or protoplasm). 



In so far as normal physiology is concerned, we shall exclude pathological 

 changes and accept as growth an increase in size only in so far as it remains within 

 "normality", as is implied in Rossle's definition. We do not consider the notion 



Literature p. 253 



