156 GROWTH PRINCIPLES AND THEORY 2 



in entropy in a closed system is always positive or, as we may also say, order is 

 continually and increasingly destroyed. But in an open system and a living 

 organism in particular, there is not only entropy production owing to irreversible 

 processes, but the organism feeds, as Schrodinger (1944) has said, on negative 

 entropy. It imports complex organic molecules with high free energy, breaks 

 them down, and gives the simpler end products back to environment, partly 

 using the free energy so gained for maintaining and building up higher order. 

 In this way, living systems can avoid the increase of entropy and loss of order and 

 maintain themselves at a constant entropy level of the steady state. They may 

 even advance, in development and evolution, toward states of higher order and 

 differentiation. 



The classical second law is not violated but holds true for the organism plus its 

 environment. This, however, does not obviate but rather emphasizes the necessity 

 of a thermodynamics of open living systems. The statement that there is an 

 overall increase of entropy tells nothing about the functioning of any particular 

 system. As it is necessary to develop the thermodynamics of heat engines, re- 

 frigerators or chemical reactions in each particular case, the same is true of open 

 systems and living organisms, taken as a whole or in their component processes. 

 This is a difficult and important task which today is in its beginnings. 



(j) Dynamic morphology 



Every living system is maintained in continuous flow, degeneration and renewal 

 of its components. What appears to be a persistent structure at one level is 

 maintained in a continuous exchange, production, growth, and death of systems 

 at the next lower level : of chemical compounds in the cell components, of cell 

 components in the cell, of cells in the multicellular organism. Hence the postulate 

 of a dynamic morphology (BertalanfTy, 1941 a) arises: Living systems, forms, and 

 structures have to be considered the result and expression of an ordered flow of 

 processes, the laws of which are to be discovered. Modern experience justifies the 

 classical dictum of Claude Bernard (1865): "The synthetic activity by which 

 the organism maintains itself is of the same nature basically as that by which it 

 regenerates after a lesion or reproduces and multiplies. Organic synthesis, repro- 

 duction, regeneration, integration, wound healing" (and, as we may add, growth) 

 *'are only diflferent aspects of a single phenomenon." 



III. CELL GROWTH AND MULTIPLICATION 



The growth of organisms takes place by growth and multiplication of cells 

 (generally in the way of mitosis), and formation of metaplasmic and paraplasmic 

 products. A review of these topics in their biochemical, physicochemical and 

 morphological aspects is beyond the scope of the present study. Only a few 

 quantitative or quantifiable relationships in cell growth will be discussed briefly. 



(a) Nuclear growth and nuclear series 



The average DNA content of the nucleus is constant in diploid somatic cells 



