CHAPTER 3 



The Organism as Machine 



3/1. In accordance with S. 1/11 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 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, one of the essential 

 events 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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