ii.] COLOURED LIGHT 35 



white and black, red and green, yellow and blue. And whether 

 or no we happen to believe that, e.g., a red light is katabolic and 

 a green light anabolic, we assuredly do believe in what has been 

 termed by Bernard the axiom of general physiology that 

 katabolic analysis and anabolic synthesis are inconceivable apart 

 from each other. I think that we should not hastily admit that 

 our double electrical change is presenting us to another aspect 

 of a familiar if somewhat nebulous colour theory ; I think we 

 have no ground for assuming that our conclusion means any- 

 thing more than the old axiom behind a new face. A process 

 necessitates the anti-process, and if the process is attended 

 by an electrical change of given sign, we may expect that 

 the anti-process will entail an electrical change of opposite 

 sign. The chemical changes taking place in living matter are 

 in general reversible changes. 



18. Complementary colours. One question we may indeed 

 put to the test before passing on. We may see whether or 

 no complementary colours have opposite electrical effects, and 

 whether the excessive action of a given colour favours or dis- 

 favours the action of its complementary. I have tried both 

 these points ; I had no real expectation that red and green 

 light, e.g., should have electrical effects of opposite signs, nor 

 that the excessive action of a given monochromatic light would 

 promote the subsequent action of its complementary. And in 

 point of fact, neither of these things happened. The effects 

 of all sorts of colours were of the same sign. The joint effect 

 of two complementary colours was practically the sum of their 

 separate effects. And the prolonged excessive action of a 

 given colour fatigued the retina to that colour just as much o/ 

 as little as to the complementary colour. All colours, in fact, 

 as regards the electrical response they elicit from the retina, 

 give that response of the same sign, and seem to act in the same 

 direction, more or less powerfully according as they are more 

 or less luminous. Thus, e.g., in a given series of trials, the 

 responses came out of the following relative magnitudes : 



Red . . . +4 

 Yellow . . . + 16 

 (White). . . +33 



Green . . . + 1 2 

 Blue , , , +9 



