Intramural vessels and endothelial cells in the walls of sclerosed retinal arteries.

ARTERIO-SCLEROTIC vessels are clinically and histologically important. I have studied retinal material, especially the tissue of fatty change for a great number of years. The chemical nature of the fat is still practically unknown. I have now studied sclerosed retinal arteries systematically. First I examined the unstained tissue, then I used the technique of retina in bulk. Later I combined the bulk technique with staining, mainly with haematoxylin, Weigert, or sudan red. It seems to be important that the first vasa vasorum shown in the retina of the human eye were in the walls of these sclerosed retinal arteries. (Loew-enstein, 1947 a, b; 1948 a, b.) In the literature, intramural vessels in the ascending aorta and in the coronary artery have been described by Robert (1929), who found a discrete capillary system in the intima of the aorta. Paterson (1936) mentioned vascularization of coronary arteries in association with arterio-sclerosis. It is most important that Paterson never discovered intramural vessels in normal arteries. As far as I understand him, he did not find any newly formed vessels in the arteries either of humans or of normal animals. Winternitz and otthers (1938), produced a perfect specimen demnonstrating the vasa vasorum in sclerosed coronary arteries. The tissue of the arteries was cleared and injected with black ink, and showed the presence of a typical network of vasa vasorum ill the rich vascular system of the intima. Of course, it is much easier to work on these huge arteries than on our small retinal vessels. But I frequently found intramural vessels in the retina, especiallyN as our technique improved. The fine sclerosed vessels came out very clearly, especially with reduced light and frequent change of thet iris diaphiragmi. We know, of course, that cases of arterio-sclerosis appear clinically as a ramified rete mirabile. Ballantyne (1949) has shown typical retinal and preretinal vessels by ophthalmoscopic examination. In our histological material we demonstrated new vessels, the " vasa vasorum". This material was mostly arterio-