There is hardly a hysterical subject whose retina is not partly insensitive.[40] As a rule the insensitive parts are connected, and include the outer half of the retina. In these cases the field of vision is more or less contracted, and appears to him not as it does to the normal man--as a circle--but as a picture bordered by whimsically zigzag lines. Often, however, the insensitive parts are not connected, but are scattered in isolated spots over the entire retina. Then the sufferer will have all sorts of gaps in his field of vision, producing strange effects, and if he paints what he sees, he will be inclined to place in juxtaposition larger or smaller points or spots which are completely or partially dissociated. The insensitiveness need not be complete, and may exist only in the case of single colours, or of all. If the sensitiveness is completely lost (‘achromatopsy’) he then sees everything in a uniform gray, but perceives differences in the degree of lustre. Hence the picture of nature presents itself to him as a copper-plate or a pencil drawing--where the effect of the absent colours is replaced by differences in the intensity of light, by greater or less depth and power of the white and black portions. Painters who are insensitive to colour will naturally have a predilection for neutral-toned painting; and a public suffering from the same malady will find nothing objectionable in falsely-coloured pictures. But if, besides the whitewash of a Puvis de Chavannes, obliterating all colours equally, fanatics are found for the screaming yellow, blue, and red of a Besnard, this also has a cause, revealed to us by clinical science. ‘Yellow and blue,’ Gilles de la Tourette[41] teaches us, ‘are peripheral colours’ (_i.e._, they are seen with the outermost parts of the retina); ‘they are, therefore, the last to be perceived’ (if the sensitiveness for the remaining colours is destroyed). ‘These are ... the very two colours the sensations of which in hysterical amblyopia [dulness of vision] endure the longest. In many cases, however, it is the red, and not the blue, which vanishes last.’