The author describes the physical and physiologic characters of "Grenz" or borderline rays so named because they lie in the spectrum at the lower limit of the roentgen rays. Their wavelength is from 1 to 3 Angström units. In penetrability they are so soft that their absorption in air is appreciable. Their therapeutic use is therefore limited to superficial lesions of the skin and to certain systemic diseases in which an erythema acts favorably.
No extravagant claims are made as to the curative effect of the rays. Preliminary reports are made in a considerable list of diseases of the skin in which the results of other radiotherapy are already known. In a goodly number of these, excellent results are claimed. Another list names conditions in which good results were obtained. In a third list bad results are acknowledged.
The Grenz rays are said to present less dangers than the roentgen