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The present investigation was undertaken in order to provide a necessary ultrastructural basis for the complete interpretation of recent findings on the electrophysiology of the sheep retina and on the influence on retinal function of certain drugs and toxic substances. The sheep retina was shown to be a mixed retina with a rather large number of cones. The receptor cells were conventional in shape. Typical differences in light and electron optical density between rod and cone ellipsoids could be explained as differences in stainability of the mitochondrial content. Specific connections between the outer segment disks and the plasma membrane as well as the occurrence of phagosomes in the pigment epithelial cells are discussed in relation to the development and the renewal of the receptor outer segment. No melanin granules were seen in the pigment epithelium of the investigated specimens, which were all taken from the tapetal area of the fundus. The possible relation between lipid-like bodies in the pigment epithelium and vitamin A metabolism is discussed.

Green monkey kidney (GMK) cells were inoculated with vaccinia or herpes simplex virus, and the effect of photodynamic treatment with proflavine and light was studied in the electron microscope. Whereas virions were abundant in all untreated cultures (incubated with virus for 15 hours or more), no virus particles could be found in the treated ones. Proflavine and light, in the amounts used, seemed to exert a certain degree of toxicity on the GMK cell cultures, but virus reproduction was effectively stopped by the treatment. Preliminary results on photodynamic treatment of human herpes keratitis are mentioned.

The present paper describes in detail a new method developed for d.c. registration of the human ERG. In this way it was possible to investigate retinal functions that have not earlier been studied clinically, e.g. the retinal responses below the b-wave threshold, the c-wave and other slow potentials after cessation of the light stimulus. It is suggested that the method might lead to an earlier diagnosis than before of certain retinal and pigment epithelial disorders induced by drugs or based on other pathological conditions.