CHAPTER 3 



The Animal as Machine 



3/1. We shall assume at once that the living organism in its 

 nature and processes is not essentially different from other matter. 

 The truth of the assumption will not be discussed. The chapter 

 will therefore deal only with the technique of applying this 

 assumption to the complexities of biological systems. 



The numerical specification of behaviour 



3/2. If the method laid down in the previous chapter is to be 

 followed, we must first determine to what extent the behaviour 

 of an organism is capable of being specified by variables, remem- 

 bering that our ultimate test is whether the representation can 

 be by dial readings (S. 2/3). 



There can be little doubt that any single quantity observable 

 in the living organism can be treated at least in principle as a 

 variable. All bodily movements can be specified by co-ordinates. 

 All joint movements can be specified by angles. Muscle tensions 

 can be specified by their pull in dynes. Muscle movements can 

 be specified by co-ordinates based on the bony structure or on 

 some fixed external point, and can therefore be recorded numeric- 

 ally. A gland can be specified in its activity by its rate of 

 secretion. Pulse-rate, blood-pressure, temperature, rate of blood- 

 flow, tension of smooth muscle, and a host of other variables can 

 be similarly recorded. 



In the nervous system our attempts to observe, measure, and 

 record have met great technical difficulties. Nevertheless, much 

 has been achieved. The action potential, the essential event in 

 the activity of the nervous system, can now be measured and 

 recorded. The excitatory and inhibitory states of the centres are 

 at the moment not directly recordable, but there is no reason to 

 suppose that they will never become so. 



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