As, practically speaking, the colour vision of X. is confined to blue and white, it is of interest to note the difference in luminosity at the different parts of the spectrum that is registered by him and by P., who had blue (violet) monochromatic vision. To facilitate the comparison, the luminosity curve of the latter is shown in the diagram. [Illustration: FIG. 37. The thin line curve is the normal curve.] Perhaps another case of a patient suffering from tobacco blindness may be quoted, as it will show the differences that exist in recognising the colours of the spectrum, and that the shorter the visible limit of the spectrum at the red end, the more pronounced is the extent of the colour blindness. G. suffered from a very well-marked tobacco scotoma, occupying a considerable area. His curve of luminosity of the spectrum is shown in Fig. 37. The horizontal band beneath will show the colours which the spectrum colours appeared to match. TABLE OF LUMINOSITY FOR G. _See_ page 153. -------------------------------------------------+ Scale No. | +---------------------------------------------+ | Wave-length. | | +--------------------------------------+ | | Reading. | | | +---------------------------------+---------------- | | | | Colour of | | | Colours named by G. | spectrum to the | | | | normal eye. ---+ -----+----+---------------------------------+---------------- 57 | 6423 | 0 | | Scarlet. 55 | 6242 | 3 | No colour | 53 | 6074 | 11 | Colour “yellow,” white “blue” | Red-orange. 51 | 5919 | 34 | „ „ „ „ | Orange-yellow. 50 | 5850 | 60 | „ „ „ „ | 49 | 5783 | 64 | Colour “gold,” white “sky-blue” | Yellow. 45 | 5538 | 59 | | 40 | 5270 | 40 | Both white | Green. 35 | 5042 | 18 | „ | 30 | 4848 | 10 | „ | 29 | 4807 | 6 | Colour “very pale blue,” | Blue. | | | white as white | 26 | 4707 | 4 | Colour “blue,” white “white” | 20 | 4518 | 3 | „ „ „ „ | 10 | 4248 | 2 | „ „ „ „ | Violet. ---+------+----+---------------------------------+----------------