Congenital colour blindness can at once be discovered, and its possessor be excluded from any post in which normal colour perception is necessary, but with this type a single examination is no safeguard, as it may be developed at any period of a man’s career. The disease is, I believe, a progressive one, and at first is most generally unrecognised, the deficiencies of vision being usually slight at its commencement. It is very often brought to the notice of the sufferer by finding he is unable to read. The words at first seem only slightly indistinct, but later become undecipherable, and as time goes on he is unable to even see the letters. He or his friends then usually think it time to consult the specialist. In tobacco amblyopia the area of insensibility is central, and it may subtend a very small angle or one which covers a considerable portion of the field. I am not aware that it ever extends over it all, but it very generally covers the yellow spot. Now as the eye naturally receives the image on the centre of the retina, it follows that, as the ability to distinguish some colours is absent in that particular region, the patient is practically colour blind, though he can distinguish them on most parts of the retina which are not affected. As regards form vision, it was mentioned in the first chapter that in a healthy eye it is much more acute at the centre than towards the periphery, and instances were given of the angular distances apart that black dots on a white ground were required to be placed to allow their being seen as separate objects when the images were received on the centre of the retina, and at the periphery. Sharp definition may be said to be almost confined to 3° of angular distance at the centre, and most probably this is a happy state of affairs, for if we could see equally distinctly with the whole field of vision, the mind would be distracted from the object which it wished primarily to contemplate.