PERHAPS no more unexpected accidents ever happened than those which were announced upon the very heels of the first use of x-rays. It was as astonishing as the rays themselves that exposure without painful sensation, to what is apparently a form of light, could cause damage to tissues, which under certain circumstances might amount even to necrosis. There is no analogous clinical fact from which the occurrence of the severer forms of x-ray injuries might have been foreseen. It was a new phenomenon. There was at first no thought of caution and, as a result, reports of injuries came thick and fast during the early and enthusiastic use of the rays, so that it did not take long for all the forms of injury which are now known, to be reported. Indeed, about all of the injuries of consequence that have occurred, occurred during this early period of incautious use.