126 



BIOLOGICAL EFFECTS OF RADIATION 



Visible Ul + ra-Violct 

 I I I . I 1 I I. I L 



ai 



0.2 



0.3 0.4 0.5 0.6 0.70.8091 



Wave- Number 



Fig. 2. — Graphs of physical and biological phenomena in the visible and near visible. 

 Upper section: Absorption, a, Water, ultra-violet, visible, and infra-red. Ordinates: 



Transmissive exponents k in 



/ =h,e- 



(outside left). Thickness transmitting half 



intensity in centimeters (inside left). Transmission of 1 cm. thickness (right). Abscissas: 

 Wave-lengths in microns, /Li (bottom). Wave numbers, waves per centimeter, h. Water, 

 X-ray (same ordinates). Wave-lengths in Angstroms (instead of microns as indicated at 

 bottom), c. Ozone (same coordinates as in o; gas at standard conditions). Atmospheric 

 transmission is equivalent to about 3 mm. and can be found by shifting scale (right) up by 

 approximately half a division. 



Middle section: Radiation. Relative emission from body at 1,000°K. (dull-red thera- 

 peutic lamp). Relative emission from body at 3,000°K. (high-temperature tungsten 

 lamp). Relative emission from sun. Relative emission from mercury arc in quartz. 



Lower section: Biological phenomena, a. Transmission of flesh (^ cm. thick) in per 

 cent. 6, Relative visibility, c. Relative phototropism. d. Vitamin A. Absorption and 

 vitamin value disappears when radiated, e, Ergosterol. Absorption disappears under 



