Transcriber’s notes: The text of this e-book has been preserved as in the original, except for the correction of a single typo (ests → test), the insertion of a missing footnote anchor and the shifting of footnotes below the relevant paragraph. Italic text is denoted by _underscores_, and bold text by =equals= symbols THE HUNTERIAN LECTURES ON COLOUR-VISION AND COLOUR-BLINDNESS THE HUNTERIAN LECTURES ON COLOUR-VISION AND COLOUR-BLINDNESS _Delivered before the Royal College of Surgeons of England on February 1st and 3rd, 1911_ BY PROFESSOR F. W. EDRIDGE-GREEN M.D.Durh., F.R.C.S.Eng. BEIT MEDICAL RESEARCH FELLOW KEGAN PAUL, TRENCH, TRÜBNER _&_ Co., Ltd. 43 GERRARD STREET, LONDON, W. 1911 PREFACE As there are many who are interested in the subject of vision and colour-blindness who are not acquainted with the structure of the eye, I will give a few details so that these persons may be able to consider the problem from the point of view of these lectures. The eye is very similar to a photographic camera, and an actual image is formed on the back of the eye just as it is on the plate of the photographic camera or on the view-finder. The eye possesses a lens and also an iris which acts as an adjustable stop and regulates the size of the pupil. The membrane at the back of the eye upon which the image is formed is called the retina. The retina has several layers, but the sensitive layer consists of two elements called, from their shape, rods and cones. The problem therefore which has to be considered is, how is the light which forms the image on the sensitive layer of the retina transformed into visual impulses? Those who are interested in the subject will find further details in my book on _Colour-Blindness and Colour-Perception_ in the International Scientific Series. In that book there are three plates which show how the colour-blind see colours. I have been annoyed to find that unauthorised persons have made lanterns professing to be mine but grossly inaccurate. The sole makers are those mentioned on page 53 in this book. F. W. Edridge-Green. The Institute of Physiology, University College, Gower Street, London. CONTENTS LECTURE I THE THEORY AND FACTS OF COLOUR-VISION AND COLOUR-BLINDNESS PAGE THE VISUAL PURPLE THE ESSENTIAL FACTOR IN VISION 11 1. Anatomical Evidence 11 2. Physiological Analogy with other Body Cells 12