Volume 5

Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose.

Date:
1909-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose. Source: Wellcome Collection.

    9/190 (page 125)
    COLOUR VISION AND ITS ANOMALIES Introductory and Historical. Any attempt to give a complete account of the efforts which have been made throughout the ages to explain the nature of vision and of colours would be quite outside the scope of this work, for the subject is one of great complexity, belonging equally to the physicist, the physiologist, the psychologist, the ophthalmologist, the comparative anatomist and the pathologist, all of whom, or their predecessors, have been at work upon it since a very early date. This book is intended primarily for the student who is interested in the inheritance of colour-blindness, and we propose to give him a skeletal account only of the historical aspect of the subject of colour vision with a brief description of the colour vision of the normal eye, the modification of colour vision under pathological conditions, the phenomena of accidental colours 1 and of congenital colour-blindness. At the outset of any historical sketch of the subject we think sympathetically with Galen, who says in this connection: “We have now spoken of almost everything con cerning the eye except one single matter which indeed I had rather not describe at all, so that neither the difficulty of the explanation nor its length might cause me to be hated 2 ”; or again, when we try to arrive at a conclusion concerning the strength or weakness of the theories which have been built up and ever modified in an attempt to make them more consistent with later observed facts, we realise that, though this process has been at work since long before the time of Galen, few of us have much more confidence in the stability of our ‘visions’ than he had when he said—“Let us not dream too long, 0 brethren, nor too deeply, lest our beatific visions turn into insufferable nightmares 3 .” We shall consider first the contributions to our knowledge derived from the early Greek writers; for if it be true that Alcmaeon, who lived about 500 b.c., first practised dissection, it can be of little use to consider theories held before that date. In the pseudo- Hippocratean treatise Ilepi ’S.apKwv we are told that the connection between eye and brain is formed by a vein passing from the membrane which covers the latter to each of the two eyes and that the substance of the brain is prolonged through this vein into the eyeswhere it forms the transparent membranes which cover them; in this transparent membrane, we are told, the light and all bright objects are reflected and by this reflexion we see 4 . Surely then, if we consider with certain authorities that these views may be attributed to Alcmaeon, whom w T e know to have dissected eyes, we may give to him the credit of possibly first realising that the image of objects seen is formed in 1 See p. 137. 2 Galen also writes: “I would explain to thee in few words, O thou hideous blasphemer of Nature, if I did not well know that thou would’st contradict when I come to explain the act of vision.” 3 For these picturesque, if free, American translations from Galen see Bibl. No. 377. For the original references see Bibl. No. 6, Lib. x, Cap. 12. 4 Bibl. No. 299, p. 12; see also Hippocrates, Omnia Opera. Francofurti, 1624, p. 253. B. T. 17