APPENDIX

Although the aims of the present study have been a chemically and histologically orientated investigation on the precorneal film and the corneal surface, it would perhaps nevertheless seem incomplete if the subjective, or the so-called endoptic, observations were completely left out. It is under certain conditions possible to observe one's own corneal epithelium as well as particles in the precorneal film. Of course, it could be pointed out that such formations on the surface of the eye cannot be termed 'endoptic" in the proper sense of the word, but Tscherning, M. (1924) includes them under endoptic phenomena, and, as already mentioned, Rollet, /. (1936) considers the precorneal film to be part of the eye. According to Tscherning, a good and easy method for endoptic observations is to place a strongly luminous point in the anterior focal point of the eye, i. e. about 12 mm in front of an emmetropic eye. Rays of light from this point will after refraction in the precorneal film pass through the pupil as approximately parallel rays. Opacities in the ray path may therefore throw shadows on the retina. In movements of the eye, opacities in front of the pupil will be seen to move in the "correct" direction, whereas opacities behind the pupil will move in the opposite direction. In practice, a metal capsule from a wine bottle can be used, in the bottom ot which a small hole has been pierced with a needle. If the capsule is held closely against the eyelids, the eye's sensitivity to light will be considerably increased. In the darkness a light, round spot will be seen, the edge of which must of course be the edge of the pupil. That it is in fact the edge of the pupil that delimits the luminous spot is quite evident from the fact that the spot will alter in size if the pupil is altered in size, e. g. in consensual light reaction elicited from the other eye (Tscherning, 1924). In the luminous spot various shadows are seen, most clearly of structures posteriorly in the eye, less clearly of structures in the anterior part. Strpctures in the precorneal layer of liquid can, however, be seen under certain conditions. Already Helmholtz (1896) has depicted how particles on the surface of the cornea can be seen as mobile light dots. Tscherning explains that they appear light with dark edges because the particles project from the surface, thus acting as small concave-convex lenses focusing the light on the retina. Tscherning