VISIBLE AND NEAR-VISIBLE RADIATION 



205 



therapeutic value. Consequently, the establishment of a system based 

 on erythemal effectiveness must not be viewed as a solution to the 

 problem of measurement in the ultra-violet for general biological 

 application. 



I- 

 a 

 oc 

 o 

 in 

 m 

 < 



2500 



4000A 



3000 350O 



WAVE LENGTH 

 Fig. 35. — Vitamin A absorption and special detector. Full-line curve — absorption 

 curve of vitamin A. {Morton and Heilbron.) Dotted curve — relative sensitivity of 

 thorium photocell + pyrex, 4-mm. thickness 



0.4 



0.6 



0.8 



1.4 



1.6 



1.0 1.2 



Wave Length 



Fig. 36. — Flesh transmission and special detectors. Full-line curve F — transmission 

 of 5.0-mm. thickness of flesh. {Cart-wright, Forsythe et al.) Dotted curve C — thermo- 

 couple with filters, amethyst -|- heat resisting yellow shade yellow. Dash-dot curve T — 

 thalofide cell. 



Vitamin A. — The absorption of vitamin A is shown in Fig. 35 (54) 

 Energy absorbed in this band contributes to the destruction of the 

 biologically active material. The absorption curve can be closely 

 approximated as indicated by the dotted curve. Such a selective 

 detector would be valuable in evaluating the destructive component of 

 sources used in irradiating materials such as foodstuffs. 



