LIGHT THERAPY MAYER 399 



light. The clinical results with solar exposures have been most 

 favorable in the hands of these workers. Sunlight possesses an 

 advantage in the favorable psychic reaction which makes the patients 

 much more willing to submit to prolonged periods of exposure. Yet 

 there is empiric evidence and theoretical basis for expecting very 

 favorable therapeutic results with other combinations of light rays.*^ 

 Aside from the calcium-deficiency diseases such as rickets and tetany, 

 the favorable clinical results with radiation can not be ascribed only 

 to the vital ultra-violet region. In fact, even in bone and joint 

 tuberculosis there is now impressive evidence indicating the impor- 

 tance of the visible radiation and the wave-length region lying 

 between 320 and 390 millimicrons.*^ 



Quartz Tnercury vapor arc light. — About 0.1 per cent of the total 

 output of the energy of sunlight is in the short wave length ultra- 

 violet rays, the variation dependent on the geographic location, 

 season of year, time of day, and kind of weather; but the total 

 output of the solar " near ultra-violet " is large when one considers 

 the total intensity of sunlight.*^ As against the mercury arc, it 

 lacks the short ultra-violet rays below 290 millimicrons. The quartz 

 mercury vapor arc lamp emits a marked preponderance of ultra- 

 violet energy in relation to its total output. It emits relatively much 

 less visible and infra-red energy than does sunlight; most of the 

 infra-red comes from the heated quartz, the electrodes, the supports, 

 and the reflecting hood.** About 17 per cent of its ultra-violet rays 

 (the total ultra-violet being considered 100 per cent) are of shorter 

 wave lengths than the lower limit of sunlight. The lower limit of 

 its radiation is 185 millimicrons, but in therapy it is rarely below 

 200 millimicrons. Its upper limit of radiation is about 12 microns 

 in the infra-red. The radiation less than 450 millimicrons repre- 

 sents two-thirds of all radiation below 1.4 microns. It consists of 

 a weak continuous spectrum down to 250 millimicrons and a number 

 of spectral lines of high intensity from 450 to 185 millimicrons. 

 Quartz allows the transmission of the rays from 185 to 320 milli- 

 microns which are not transmitted by window glass. The intensity 

 increases rapidly in the first few minutes to reach the final value in 



*i Maughan, G. H., Amer. Journ. Physiol., vol. 87, p. 381, December, 1928. Sonne, 

 Carl, Arch. Physical Therapy, vol. 10, p. 139, April, 1929. Reerlnk, E. H., and Wljk, 

 A. v., Biocbem. Journ., vol. 23, p. 1294, 1928. Steenbock and Black (footnote 27). 

 Hess, A. F., and Weinstock. Mildred, idem, vol. 62, p. 301, December, 1924. Huldschinsky, 

 K., Deutsche med. Wchnschr., vol. 45, p. 712, June 26, 1919 ; Zeitschr. f. Kinderh., vol. 

 26, p. 207, September, 1920. Howland, J., and Marriott, W. M.. Quart. Journ. Med., vol. 

 11, p. 289, July, 1918. Bakwin, Harry, and Bakwin, Ruth M., The Dosage of Ultra-Violet 

 Radiation In Infants with Tetany, Journ. Amer. Med. Assoc, vol. 95, p. 396, Aug. 9, 

 1930. Casparis, H., and Kramer, B., Bull. Johns Hopkins Hosp., vol. 94, p. 219, July, 

 1923. 



*2 Phelps, W. M., Journ. Bone and Joint Surg., vol. 12, p. 253, April, 1930. 



" Coblentz, W. W., and Kahler, H., Bur. Standards Sci. Pap. 378, 1920. 



" Coblentz, W. W., Long, M. B., and Kahler, H., Bur. Standards Sci. Pap. 330, 1918. 



