36 THE SIGNS OF LIFE 



In other trials the responses were : 



[LECT. 



To Red alone . + 5 



To Green alone . + 10 



To Red and Green conjoined + 14 

 (To White) . . . +40 



19. Cause: effect. I have upon more than one occasion 

 taken records of the series of electrical effects elicited by a 

 series of illuminations of arithmetically increasing and de- 

 creasing strengths. The general question to which this special 

 question belongs is in my opinion one of fundamental elemen- 

 tary importance, coming under our notice in almost every pro- 

 vince of study, sometimes in simple and accessible shape, 

 sometimes disguised or hidden by the manifold circumstances 

 and accessories of organic life. 



The question is : What quantities of physiological effect, Y, 

 are elicited by given quantities of physical cause, X ? And the 

 answers to that question in its various forms will be most 

 conveniently and symmetrically expressed by a curve to the 

 co-ordinates OX, OY, with the physical cause or stimulus or 

 excitation plotted along OX, and the physiological effect 

 along OY. 



Generally speaking, we cannot hope to reach in physiological 

 matters an accuracy such as is possible in physical matters. 

 Our data are too rough, perturbed by too many uncontrollable 

 variables, and may not as a rule be formulated in mathemati- 

 cally correct curves characterised by simple equations. The 

 well-known logarithmic law of sensation is at best of very 

 limited application, and a sensation curve actually plotted from 

 experimental data exhibits great divergences from any loga- 

 rithmic curve that can be fitted to it. Without, however, making 

 any attempt to trim or strain experimental results and fit them 

 with orthodox mathematical curves, we may with advantage 

 plot them out to scale on a simple system of co-ordinates OX, 

 OY, and thus recognise at a glance whether, within the range of 

 the observations made, a given physiological effect has varied 

 (i) as its cause, or (2) more rapidly than its cause, or (3) less 

 rapidly than its cause. I mean of course exciting or proximal 

 efficient cause or stimulus, and not the whole previous chain of 

 principiants resulting in the particular event 



