G. was tested for light sense by the extinction method, and it appears that the final sensitiveness to light at the central part of the eye was nearly 12 times less than a person possessing normal sense. I may mention that I have examined one, if not two cases in which the patient was not only tobacco blind, but also congenitally colour blind. Though interesting for record, they need not be given in full here. With these specimens of examination I must leave the cases of tobacco blindness. Although very important, they by no means constitute the sole cases of colour deficiency due to disease. I will give as an instance a case of loss of colour sensation due to progressive atrophy of both eyes which was examined, with Mr. Nettleship’s aid. When tested with spectrum colours--a patch of white light being placed in juxtaposition with the colour--it was found that W. S. was absolutely blind to colour from 26·75 (λ 4733) on the scale of the spectrum to the termination of the red of his spectrum, which was close to 63 on the scale (λ 7082). Above scale No. 26·75 W. S. saw blue, and his spectrum was continued normally in the violet. His luminosity curve (Fig. 37) was made without any difficulty, and, compared with my own, shows a slight deficiency in brightness from the red to the yellow, but his perception of luminosity increases as the blue is approached. TABLE OF LUMINOSITY FOR W. S. _See_ page 155. ---------+------------+---------+---------+---------- | | | Spectrum| Spectrum | | | colours | colours | | | named | to normal Scale No.|Wave-length.| Reading.| by W. S.| eye. ---------+------------+---------+---------+---------- 60 | 6728 | 3·4 | Grey | Scarlet. 58 | 6520 | 15·0 | „ | 56 | 6330 | 41·0 | „ | 55 | 6242 | 43 | „ | 54 | 6152 | 69 | | 52 | 5996 | 94 | | 50 | 5850 | 100 | „ | Orange. 48 | 5720 | 96 | | 45 | 5538 | 88 | | 42 | 5373 | 74 | | 40 | 5270 | 61·5 | „ | Green. 38 | 5172 | 45 | | 35 | 5042 | 30 | | 30 | 4848 | 12 | „ |Blue. 25 | 4675 | 6 | Bluish | 20 | 4518 | 4 | | 15 | 4376 | 3 | Blue | Violet. 10 | 4248 | 2·5 | „ | ---------+------------+---------+---------+---------- He was subsequently tested with colour discs--Ultra-marine (U), Red-royal (R), Emerald-green (G), Chrome-yellow (Y), White (W), and Black (B). It was found that-- 165 (U) + 48 (R) + 147 (G) = 75 (W) + 285 (B). The black reflected 3·4 of white; hence the true equation is--