THE MACHINE WITH INPUT 4/5 



parameters thus include the conditions in which the organism hves. 

 In the chapters that follow, the reader must therefore be prepared 

 to interpret the word "input" to mean either the few parameters 

 appropriate to a simple mechanism or the many parameters appro- 

 priate to the free-living organism in a complex environment. (The 

 increase in the number of parameters does not necessarily imply any 

 diminution in the rigour of the argument, for all the quantities 

 concerned can be measured with an accuracy that is bounded only 

 by the experimenter's resources of time and money.) 



Ex. 1 : An electrical machine that receives potentials on its two input-terminals 

 is altered by having the two terminals joined permanently by a wire. To 

 what alteration in T^b would this correspond if the machine were represented 

 as in Ex. 4/3/3 ? 



Ex. 2: "When an organism interacts with its environment, its muscles are the 

 environment's input and its sensory organs are the environment's output." 

 Do you agree ? 



4/5. Transient. The electrical engineer and the biologist tend to 

 test their systems by rather different methods. The engineer often 

 investigates the nature of some unknown system by submitting it 

 to an incessant regular change at its input while observing its output. 

 Thus, in Fourier analysis, he submits it to prolonged stimulation 

 by a regular sinusoidal potential of a selected frequency, and he 

 observes certain characteristics in the output; then he repeats the 

 test with another frequency, and so on; eventually he deduces 

 something of the system's properties from the relations between the 

 input-frequencies and the corresponding output-characteristics. 

 During this testing, the machine is being disturbed incessantly. 



The biologist often uses a method that disturbs the system not at 

 all, after the initial establishment of the conditions. Thus he may 

 put a piece of meat near an ants' colony and then make no further 

 change whatever — keeping the conditions, the parameters, constant 

 — while watching the whole evolution of the complex patterns of 

 behaviour, individual and social, that develop subsequently. 



Contrary to what is observed in living systems, the behaviour 

 of mechanical and electrical systems often settles to some uniformity 

 fairly quickly from the moment when incessant change at the input 

 stops. The response shown by the machine after some disturbance, 

 the input being subsequently held constant, is called a transient. It 

 is important to appreciate that, to the engineer, the complex sequence 

 of events at the ants' nest is a transient. It may be defined in more 

 general terms as the sequence of states produced by a transducer in 

 constant conditions before the sequence starts repeating itself. 



47 



