After mentioning the biological action of light rays in which measurable organic changes of the body stand in certain relationship to the influence of light ('light-influence'), the author goes into a detailed analysis of another effect of light, studied hitherto to a lesser degree, that of the psychic impression gained through light, to which he refers as 'light-impression'.

A report is presented on clinical investigations which aim to demonstrate a relationship between this kind of light effect and nervous vascular reactions in individuals in whom a special type of vasomotor reaction had been previously recognized. Besides subjective disturbances of a psychic order, objective changes referable to the vascular system, and changes in pulse frequency and rhythm as well as fluctuations in blood pressure, are objective expressions of the psychically influencing factors. Subjects for these investigations were chosen from among patients who presented conditions