The grenz rays have but recently reached the extent of administration which they deserve. Their development has been relatively slow for many reasons. At the outset, neither the apparatus nor the measurement was satisfactory. The roentgenologist does not possess the exact knowledge of cutaneous diseases in their various stages, and the dermatologist is less interested in physics and in complicated calibration technics; hence, little has been added to Bucky's1 indications and technic.
Inexpensive and useful equipment has become commercially available in recent years, and the calibration technic has been greatly improved. The practical use of grenz rays has been improved by a more exact knowledge of the biologic effects, and about ten years seems sufficient to judge the effectiveness and possible dangers of these rays.
HISTORY AND PHYSICS
The use of long wave roentgen rays for the treatment of cutaneous diseases was introduced by Schultz.2 Exact methods of