L.: A method for photographing fluorescence in circulating blood in the human retina. Circulation 24: 82

nal vasculature would be better under-stood if more were known about blood flow in these vessels. Because of the unique quality of transparency in the eye, methods depend-ing on direct observation of the retinal ves-sels seem especially inviting. Already re-ported by various authors are technics for measuring the changes in caliber of retinal vessels,1 and methods of observing retinal blood flow by cinematography,2 and, in cats, by injecting trypan blue. Although useful, these methods have certain limitations, and additional means of observing retinal blood flow with increased visibility and definition are needed. The purpose of this paper is to describe a method for the study of retinal blood flow in man by the use of intravascular fluorescein and retinal photography, and to report some preliminary observations made with this method. Materials and Methods The Zeiss fundus camera was used. It was equipped with an electronic flash, the maximum discharge of which allowed one photograph every 12 seconds. Light intensity of the electronic flash was set at position III, and retinal photographs were made of the luminescence of fluorescein as it passed through the retinal vessels. In order to do this, both activating and emitting wave lengths of blood-fluorescein mixtures were determined spectrofluorometrically. The optimal activating wave length was found to be 490 mju, in the blue range of the visible spectrum; and the maxima