Highly characteristic if not strictly specific alterations affect retinal and glomerular capillaries in patients with long-term diabetes. The morphologic characteristics of these lesions distinguish degenerative vascular disease in diabetic patients from that in nondiabetic individuals. Their presence differentiates the pattern of vascular degeneration in the retina and kidney from that so far demonstrated anatomically elsewhere in diabetic patients in whom these characteristic lesions occur. While there is disagreement among authorities, some regard the development of capillary lesions as an integral component and inevitable accompaniment of long-term diabetes, rather than as one of its complications. Glomerular lesions are found in about 50 per cent of patients with retinal capillary involvement and are not present in patients without retinal lesions. Conversely, if they are looked for, retinal lesions are found in practically all patients with glomerular lesions. Thus there is a definite correlation between the incidence of retinal and renal involvement. The lesions do not appear to be strictly comparable morphologically. It has been suggested that they reflect similar pathologic processes, the manifestations of which are modified by structural differences between the capillaries concerned. It may also be that the interpretability of changes in the retina and glomerulus is concerned. The capillary network visualized in flat mounts of whole retinas has a rather simple pattern. In the glomerulus, about 2.5 cm. of capillaries branch and reanastomose within the confines of a sphere about 200 microns in diameter. Our concepts of the finer details of normal glomerular structure and its alterations in disease are changing with recent advances in microscopic and histochemical technics.

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