II GROWTH PRINCIPLES AND THEORY I43 



II. THE ORGANISM AS AN OPEN SYSTEM 



(a) Introduction 



A modern investigation of the problem of growth must start from the fact that 

 any living organism, as well as its components, is an open system which, as a rule, 

 approaches a steady state. 



Conventional physical theory (kinetics and thermodynamics) is limited to 

 closed systems, i.e. systems that do not exchange matter with environment. How- 

 ever, the elementary fact of metabolism shows the organism to be an open 

 system, maintaining itself in continuous exchange, import and export, building 

 up and breaking down of its components. The laws of open systems are specific 

 and peculiar; their investigation has led to an important expansion and generali- 

 zation of physical theory. 



Up to recent times there was no theory applying to systems of such kind. 

 Biology and physiology rather tried to employ the principles and laws of closed 

 systems to processes in the living organism. This is true of chemical kinetics which 

 succeeded in applying the laws of reversible reactions and chemical equilibria to 

 certain partial systems or, speaking more precisely, to certain fast reactions 

 within the living organism. For example, the transport of oxygen from the lungs 

 to the blood and the tissues is based upon reversible reactions and chemical 

 equilibria between hemoglobin, oxyhemoglobin, and oxygen. In contrast, the 

 laws of chemical equilibrium are, in principle, inapplicable to the state of the 

 organism as a whole. This is shown by the trivial fact that the chemical equilib- 

 rium of proteins in the presence of proteolytic enzymes as found in every cell, 

 is the nearly complete breakdown of proteins into component amino acids. 

 However, so long as the organism is alive, it remains approximately constant in 

 a state far distant from equilibrium, in the way that degradation of high-molecular 

 compounds is balanced by a corresponding synthesis. As research with isotope 

 tracers has shown, both grovips of processes proceed at relatively high rates 

 (p. i47ff.). Approach to equilibrium means death of the organism. 



Thermo dynamic ally, the living organism appears to violate one of the fundamental 

 laws of nature. According to the second principle of thermodynamics, the general 

 trend of physical events is toward increasing entropy, eventually leading to states 

 of equilibrium with maximum entropy. Entropy, according to statistical theory, 

 is a measure of probability, and hence the trend toward increasing entropy is 

 toward a most probable distribution. The most probable distribution, however, 

 of a mixture, e.g. of red and blue glass beads or similarly of molecules with 

 different velocities, is a state of complete disorder; having separate all red beads 

 on one hand and all blue ones on the other or having, within a compartment, 

 all fast molecules, that is, high temperature, on the right side, and all slow ones 

 and low temperature, at the left, is a highly improbable state of affairs. Hence, 

 entropy increases in all irreversible processes, and the trend toward increasing 

 entropy is identical with the trend toward most probable states, leveling down of 

 existing differentiations, and states of maximum disorder. 



In contrast, the living organism is thermodynamically a system of fantastic 

 improbability. In spite of irreversible processes which are continually going on. 



Literature p. 253 



111 



II 



