884 COMPARATIVE. HISTORICAL. 



familiar with the ideas of fixation-point, field of vision, binocular single and double 

 vision. Descartes originated the hypothesis of the vibrations of the ether, which 

 were supposed to exist also in the eye, and to stimulate the nerve. The following 

 may be mentioned with regard to the different parts of the eye, and their functions: 

 The school of Hippocrates knew of the optic nerve and the lens. Aristotle (384 

 B. C.) records the fact that division of the optic nerve as a result of injury causes 

 blindness. He was familiar with after-images, mentions hyperopia and myopia, 

 states that blue eyes exhibit more vigorous iris-reactions on exposure to light 

 than dark eyes, and that man alone has cilia on both eyelids. He mentions a 

 man who was able to see visions, as Quinctilian relates of the painter Theon von 

 Lamos. Herophilus (307 B. C.) discovered the retina; the ciliary body was first 

 recognized in his school. Galen (131-203 A. D.) described the six ocular muscles, 

 the lacrimal puncta, and the tear-ducts. According to him, the retina receives the 

 impressions of light: he refers the origin of the optic nerve to the thalamus. 

 Berengar (1521) was aware of the oily condition of the lid-margins; Stephanus 

 (1545) and Casseri (1609) mentioned the Meibomian glands, which were named 

 after Meibomius (1666). Aranzi described (1586) the muscles of the lid. Fallopia 

 designated the hyaloid membrane and the ciliary ligament. Plater emphasized 

 the greater curvature of the posterior surface of the lens (1583). Aldrovardi 

 saw vestiges of the pupillary membrane (1599). 



Even in the time of Vesalius (1540) the refractive power of the lens was 

 discussed: Porta (1560) compared the eye to the camera obscura, and Maurolykos 

 the action of the lens to that of a lens of glass, but Kepler (1611) was the first to 

 show the true refractive indices of the eye, and the formation of the retinal image; 

 he believed, however, that accommodation was effected by the movement of the 

 retina backward and forward. The Jesuit father Scheiner (1619) proved, how- 

 ever, that the lens was made more convex by the ciliary processes, and he assumed 

 the existence of muscle-fibers in the uvea. At the same time he recognized the si- 

 multaneous contraction of the pupil in accommodation for near vision. He believed 

 myopia and hyperopia to be due to the curvature of the lens, and he first showed 

 the inverted image on the retina of an enucleated eye. Briggs' remark (1676), 

 " Ligamentum ciliare e fibris motricibus constans," likewise the analogous one of 

 Ruysch (1743) , led Morgagni to the correct interpretation of the process of accom- 

 modation. Edm. Mariotte recognized that the reflex from the pupil arose from 

 reflected light (1668). As to the use of glasses, there is a note as early as Pliny. 

 At the beginning of the fourteenth century, the Florentine, Sal vino d'Armato 

 degli Armati di Fir (died 1317), is said to have invented them; likewise the Pisan 

 monk Alessandro de Spina (died 1313). Kepler in 1611, and Descartes in 1637 

 were the first to explain their action correctly. Huyghens made an apparatus 

 in imitation of the eye, and showed upon it the action of glasses (1695). Tne 

 struggle of the visual fields is ascribed to Gassendus (1658). Agulonius (1613) 

 occupied himself with the horopter. Briggs (1676) surmised that single vision 

 occurred when the object formed an image on homologous fibers of the retina: 

 de Peiresc described positive and negative after-images (1634) ; v. Muschenbroeck 

 knew of the color-top (1762). Leonardo da Vinci (died 1519) was well acquainted 

 with contrast-phenomena, Otto v. Gericke (1672) with the colored shadows, 

 Kepler (1611) with irradiation. The last named explained correctly upright 

 vision, the perception of depth, and the estimation of distance. Nuck analyzed the 

 aqueous humor (1688) , Chrouet the lens (1688). De la Hire (the younger) ascribed 

 to the aqueous and the vitreous the same refractive power, and tested that of the 

 lens and the cornea (1707). Maitre-Jean referred the movement of the iris to its 

 circular and radial fibers (1707). Knowledge of the eye was greatly advanced 

 by Zinn (1755). Ruysch described the muscular fibers of the iris, Monro (1794) 

 later the sphincter of the pupil more fully. Berzelius demonstrated chemically the 

 presence of muscle-tissue in the iris. Jacob discovered the layer of rods of the 

 retina. Sommering (1791) first described the yellow spot. Ant. Leeuwenhoeck 

 knew of the lens-fibers. Reil noted the star-shaped fissility of the lens. Berzelius 

 examined chemically the lens, the aqueous, the vitreous, the pigment, and the 

 tears. Young first observed astigmatism (1801). Brewster and Chossat (1819) 

 tested the refractive power of the ocular media. Purkinje studied subjective 

 vision thoroughly (1819). Helmholtz' "Physiological Optics" summed up the 

 entire science in a classical work (1856-66). 



