Born at Culgower in Sutherlandshire in 1850, the youngest, and eventually the last survivor, of a family of four, consisting of two sons and two daughters. The Gunns are an old Scandinavian stock and have been settled for many generations in the north and north-east of Scotland. Marcus Gunn was educated for a year at the village school, and then for some time at Golspie. At the age of 14 he went to Edinburgh and received his professional training at the University, where he was a contemporary and slight acquaintance of Robert Louis Stevenson. In Edinburgh, Syme, Lister, and the ophthalmologists Walker and Argyll Robertson, were among his teachers. He also studied at St Andrews University. In 1873, having been introduced to John Couper (qv), he began attendance at the Moorfields Eye Hospital, and worked at the comparative anatomy of the eye under Professor Schafer at University College during the early part of 1874. In the summer vacation, and for part of 1875, he was in residence at the Perth District Asylum, Murthly, where he examined the fundus oculorum of lunatics, having been attracted to the subject by the published work of Clifford Allbutt. He found the eyes of lunatics to be precisely like those of the sane. He enjoyed his work, went fearlessly among the patients, but was once set upon, his assailant being an old melancholic woman, whom another lunatic pulled off. He studied at Vienna from December, 1874, to June, 1875, under Jaeger, with whom he was a favourite and whom he admired. This great teacher insisted on his class using his own form of ophthalmoscope, an improvement on the original Helmholtz model. Gunn afterwards excelled as an ophthalmoscopist. He considered Jaeger greatly superior as a teacher to Arlt and Stellwag. Returning to London, he again worked at Moorfields under Couper, being appointed Junior House Surgeon in August, 1876, and becoming Senior House Surgeon in December, retaining the post till November, 1879. His work as a resident medical officer coincided with noteworthy improvements in various directions in the hospital, such as the reform of the nursing, a higher standard of note-taking, and better results in the operations for cataract. His influence made itself felt in these matters, and the last-mentioned is perhaps to be attributed in no small degree to his early adherence to Listerian principles. A remark by Syme, in commenting upon one of Lister's cases at Edinburgh-"We are told of pus, we fear pus, we expect pus-but we see no pus"-made a great impression upon him as a student, and in John Couper he found a chief who was enthusiastically in sympathy with the new principles. He went to Australia in December, 1879, meaning especially to collect the eyes of marsupials and the Monotremata with a view to microscopic examination, and his work on this subject, partly published in papers in the *Journal of Anatomy and Physiology*, early attracted the attention of Sir William Bowman. He helped to examine the zoological specimens collected by the Challenger Expedition, and embodied much of this work in his Arris and Gale Lectures before the Royal College of Surgeons in 1888. These were not printed. Gunn was elected Assistant Surgeon to the Moorfields Eye Hospital in August, 1883, in place of John C Wordsworth (qv) resigned, becoming full Surgeon in 1888. In 1880 he was appointed Ophthalmic Surgeon to the National Hospital for the Paralysed and Epileptic, Queen Square, and to the Hospital for Sick Children, Great Ormond Street. Later he was Assistant Ophthalmic Surgeon to University College Hospital. He was Vice-President of the Section of Ophthalmology at the Edinburgh Meeting of the British Medical Association in 1898, and President of the same Section at the Toronto Meeting in 1906, and there delivered an address before the American Academy of Ophthalmology and Oto-laryngology on "Certain Affections of the Optic Nerve". He put forward the view in this address that the initial oedema of the disc in cases of cerebral tumour is due to pressure on the small veins of the pial sheath by fluid in the intervaginal space. At the time of his death Gunn was Senior Surgeon at the Royal London Ophthalmic Hospital, Moorfields; Ophthalmic Surgeon at the National Hospital for the Paralysed and Epileptic, Queen Square; President of the Ophthalmological Society of the United Kingdom; a Visitor for the King's Hospital Fund; Consulting Surgeon to the Westminster Ophthalmic Hospital; Hon Ophthalmic Surgeon to the Royal Caledonian Asylum; Ophthalmic Surgeon at the Great Northern Central Hospital and the Hospital for Sick Children, Great Ormond Street; and Assistant Ophthalmic Surgeon to University College Hospital. He died at Hindhead, after a long and painful illness, on Nov 29th, 1909, and was survived by his widow and two daughters. He practised at 54 Queen Anne Street. Apart from his daily hospital and private practice, Gunn's ophthalmic interests lay to a large extent in the physiology and pathology of the retina, optic nerve, and visual functions. Of his later work he would probably have liked best to be associated with his classical paper on the ophthalmoscopic evidence of retinal arterial sclerosis as a sign of similar changes in the arteries of the brain and other organs. He had also convinced himself of the bad prospects in life of persons with albuminuric retinitis some time before Miley's well-known paper on this subject was undertaken. Thus, in discussing before the Ophthalmological Society the differences between diabetic and renal retinitis, he said: "In my experience it is most exceptional to see an old case of albuminuric retinitis; this latter affection seems to occur at a late stage of the general disease, so that death supervenes before the retinal changes have existed very long." He first learnt this by discovering that patients with this form of retinitis who attended for demonstration usually died before the time came round for the following years' course. In speaking of unpublished work, it may be mentioned that Gunn was one of the first, if not the first, to insist on the importance of studying fine changes in the cornea and iris by the aid of the strongest available magnification, and that he has the credit of causing the introduction at Moorfields of the now commonly used high pocket magnifier. When in Vienna he had been much impressed by the systematic teaching of ophthalmology, and soon after his attainment of staff rank at Moorfields his efforts led to the establishment of regular courses of instruction in ophthalmoscopy. Other courses have since been added, and a flourishing School of Ophthalmology at the hospital is the result. Gunn was an operator of no mean skill. He extracted cataracts invariably after a preliminary iridectomy done several weeks previously, and always held that this was the safest operation. He had a high sense of the responsibility which lay upon the surgeon, and carried it to the extent of seldom allowing anyone else to perform the operations for which he himself was responsible. He was a skilful all-round ophthalmic surgeon, but it was universally felt that it was as an ophthalmoscopist he shone with the highest brilliancy. Thus he took up a reserved attitude towards retinoscopy lest it should lead to neglect of the search for slight changes in the fundus. He was an admirable teacher, and his eulogists unite in bearing witness to his charm, his simplicity, his sense of humour, and his lofty character. He was markedly intellectual, a keen observer, a man of fine judgement and mental grasp. As a reader he could rapidly extract the pith of a book, storing it in his retentive memory. He came of a typical studious Scottish stock, his father and uncles, though engaged in farming, having managed to educate themselves at the University of Aberdeen, to which they walked and from which they re-walked to their remote northern home, a distance of 200 miles there and back. He was devoted from boyhood to outdoor pursuits. He was fond of shooting, was a botanist, a marine zoologist, and a keen geologist, his collection of fossils from the Jurassic and Old Red Sandstone, which crops out in his own native district of Scotland, being exceptionally fine. The best specimens from his collection went to the Geological Department of the British Museum during his lifetime. Publications: "Minute Anatomy of the Retina."- *Jour. Anat. And Physiol.*, 1877, xi, 357. "The Eye of Ornithorhyncus."- *Ibid.*, 1884, xviii, 401. "The Embryology of the Retina of Teleosteans." - *Ann. Mag. Nat. Hist.*, 1888. "Retinal Reflexes."- *Roy. Lond. Ophth. Hosp. Rep*., 1887, xi, 348. "Continuous Electrical Current as a Therapeutic Agent in Atrophy of Optic Nerve and in Retinitis Pigmentosa."- *Ibid.*, 1882, x, 181. "Sympathetic Inflammation."- *Ibid.*, xi, 273. "Nature of Light Percipient Organs and of Light and Colour Perceptions."- *Ibid.*, 1889, xii, 101. "Peculiar Appearance in the Retina" (now generally known as 'Gunn's Dots').- *Trans. Ophthalmol. Soc.*, 1883, iii, 110. "Amblyopia from Bisulphide of Carbon."- *Ibid.*, 1886, vi, 372. "Nystagmus. Toxic Amblyopia."-*Ibid.*, 1887, vii, 305. "Growth of Lens Fibres. Foveal Reflex in Myopia."- *Ibid.*, 1888, viii, 126. "Retinal Arterial Sclerosis."-*Ibid.*, xii, xviii, xxiv. "Pemphigus of Conjunctiva."-*Ibid.*, 1893, xiii, 30; 1895, xv, 68; 1896, xvi, 45. "Haemorrhage into Optic Sheath."-*Ibid.*, 1896, xvi, 95. "Bowman Lecture on Visual Sensation."-*Ibid.*, 1900, xx, 11. Presidential Address, "History of the Ophthalmological Society."-*Ibid.*, 1908, xxviii, p. i. "Keratitis Nodosa."- *Ibid.*, 1902, xxii, 97. "Family Optic Atrophy."-*Ibid.*, 1907, xxvii, 221. "Two Lectures on Congenital Malformations of the Eye," 8vo, London, 1889; reprinted from *Ophthalmic Rev.*, 1889, viii, 193, etc. "A Case of Haemorrhagic Disease of Retina with Obliteration of Veins," plate, Helmholtz's *Festschrift*, 1893. "Diseases of the Eye" in Treves's *Manual of Surgery*. "The Eyeball and its Surroundings" in Morris's *Treatise on Human Anatomy*. "Optic Nerve and Retina."- *Encyc. Med.* *Sympathetic Inflammation of Eyeball*, 8vo, London, 1887. *Gowers's Manual of Ophthalmoscopy* (co-editor of 3rd and 4th ed.).