STATEMENT OF THE THEORY 263 



(9) The reversal of the colour of a fixated patch by addition of 

 white light. 



(10). The reversal of the colour of a patch of hght during simple 

 prolonged fixation. 



(11) The appearance of colours of fair saturation during simple 

 fixation of bright white light. 



(12) The uniocular struggle of complementary colours during which 

 they fuse at moments to give white and at other moments appear 

 separately in consciousness. 



(13) The fact that a white image, produced by uniocular fusion 

 of two complementary colours, may be followed by an after-image, the 

 character of which proves that the rays of each colour have produced 

 throughout the appropriate retino-cerebral colour-systems their specific 

 effects, and that therefore there has been no mutual destruction or 

 interference of their physiological effects. (See McDougall's Theory 

 in Section V.) 



CHAPTER II 



RESEARCHES BASED UPON THE THEORY 



We have already, in Part I, discussed many of the researches which 

 were inspired by Hering and his theory. Of these the most noteworthy 

 are those referred to under the names of Hering, Hess, and Tschermak, 

 They deal chiefly with the equivalence of colour equations under 

 different conditions, — adaptation, area and region of retina stimulated, 

 etc. — and with the facts of temporal and spatial induction. Those 

 devoted to colour mixtures have been largely polemical and directed 

 to controvert the statements of adherents of the duplicity theory or of 

 the Young-Helmholtz theory, 



Hering's theory affords an explanation of the general facts of succes- 

 sive contrast. If for example, the eye is stimulated with blue light, 

 allonomous anabolism is set up in the yellow-blue substance, and a 

 large amount of the substance is formed. If now yellow light stimulates 

 the retina katabolism is set up in this much increased material and the 

 resulting sensation is much greater than without previous stimulation. 

 The abnormal saturation of the complementary to the stimulating 

 colour is thus explained. A positive after-image is explained by a 



