146 



GROWTH 



PRINCIPLES AND THEORY 



4. A closed system in equilibrium neither needs energy for its maintenance nor 

 can energy be obtained from it. To perform work, a system must be not in 

 equilibrium, but tending to attain it. In order to go on this way, the system must 

 be maintained in a steady state. Therefore, the character of an open system is 

 the necessary condition for the continuous working capacity of the living organism. 



5. A further characteristic of open systems can also be easily seen. In conven- 

 tional physical systems, the final state eventually attained is defined by the initial 

 conditions. For example, in a closed chemical reaction system the final concen- 

 trations trivially depend on the initial ones. If either the initial conditions or the 

 course of the process is altered, the final state also will change. In open systems, 

 however, the steady state eventually reached is independent of the initial con- 

 ditions and of the course the process has taken [as, for example, can be seen from 

 equation (2.1)] and determined only by the system parameters of reaction and 

 transport. Hence, the same final state can be reached from different initial 

 conditions or in different ways. This characteristic of open systems is called 

 equifinality, and is an important characteristic of living qua open systems [cf. p. 2 1 sff.) . 



6. Closed chemical systems asymptotically approach a state of equilibrium. 

 In open reaction systems, in contrast, phenomena o^ false start and overshoot appear 

 under certain mathematically definable conditions (Burton, 1939; Denbigh et al., 

 1 948 ; Bertalanffy, 1 953) . That is, the process first takes place in a direction opposite 



Fig. 2. Overshoot and false start in open systems. Under certain mathematical conditions 

 {cf. Burton, 1939; Denbigh et al., 1948) phenomena of overshoot (^4) and false start (C, D) 

 appear even in the simplest open reaction systems, while in conventional closed systems 

 the approach to chemical equilibrium is simply asymptotic (type of curve B). The figure 

 represents approach to the steady state in a system of 2 reactants, the concentration of 

 one of which passes overshoot or false start (A, C, D) while the other {B) asymptotically 

 approaches the steady state which is assumed to be zero. If the final steady-state concen- 

 trations are higher than the initial concentrations, the curves are to be rotated around 

 the <-axis. The curves are drawn for different arbitrary values of the constants in the 

 differential equations describing the open system. Overshoot and false start can experi- 

 mentally be reproduced in suitable open reaction systems. After Denbigh et al., 1948. 



to that eventually leading to a steady state (Fig. 2). Phenomena of overshoot and 

 false start are not encountered in conventional kinetics, but are possible in the 

 kinetics of open systems and found in many physiological phenomena. 



