ii6 ANIMAL BEHAVIOUR 



In the last equation the value of the dependent variable, \\\ 

 is measured as work done, equivalent to the lifting of a mass, 

 M, through so many feet, L, or the dimensions of W are M and 

 L^/t 2. So also the calorific values of the food eaten can be ex- 

 pressed in heat (calories) which is again equivalent to a mass 

 that is lifted through a certain distance against gravity and the 

 dimensions of /),/, etc., are also M and Ly^ ^ Thus the terms on 

 both sides of the equations are of the same denominations. 



In physiological investigations we endeavour to represent all 

 organic processes by such equations, and although this is not always 

 practicable it is often possible and we must believe that, given 

 complete knowledge of all the conditions of the process studied, 

 it will always be possible and practicable. 



Let something that happens in the outer world stimulate a 

 receptor : there is no doubt that a simple physical reaction 

 between the materials and energies of the things outside and those 

 of the receptor occurs. So also the change that occurs in the 

 receptor stimulates the afferent nerve, the change, or impulse, 

 propagated in the nerve stimulates the synapse, the changes in the 

 synapse stimulate the efferent nerve and the impulse descending 

 the latter stimulates the effector organ, releasing the energy that 

 is potential in the latter, whereupon work is done. All these 

 steps in a behaviouristic process are conceivably representable 

 by equations of the form, U =f(j), q, r), where the terms on both 

 sides are of the same kind, that is, can be made to involve only 

 measurements of mass, length and time, and such equations 

 may apply to some very simple and limited types of animal 

 behaviour. 



But when the stimulation of a receptor is followed by a sensation 

 it is not possible to make any physico-mathematical relation 

 between the terms involved, for that term U cannot be made to 

 represent the sensation. It is a state of consciousness which has 

 quality, intensity and duration, but it cannot be symbolized by 

 length, mass and time. It is true that there is a relation of 

 dependence between the sensation and the physical events that are 

 associated with it — unless these physical events occur we do not 

 have the sensation. But there is not mathematical functionality 

 in the sense that the dependent variable {U = the sensation) 

 is of the same denominations as are the independent variables 

 (/), q, r = physical vibrations, say) and that for every numerical 



