as an aid to the consideration and understanding of the spectral sensitivity of the pink 

 bollworm moth, Figure 5 shows a comparison of the pink bollworm response curves 

 (low energy tests) with the sensitivity curves of the dark-adapted and light-adapted 

 human eye and the dark-adapted aphakic eye, (Source: Curves for light-adapted eye and 

 dark-adapted eye - -Encyclopedia Britannica (5); Curve for aphakic eye - -Calculated from 

 Wald (21).) 



As shown by these curves, the spectral sensitivity curves for the pink bollworm moth 

 in the visible region corresponds closely to the sensitivity curve for the dark-adapted 

 human eye since they both peak just above 500 m/i. This similarity has been pointed out 

 by Dethier (17). He also points out that these curves are nearly identical to the absorp- 

 tion curve for the chemical rhodopsin or visual purple. (Note: Visual purple is defined 

 as a purple-red pigment contained in the retinal rods of human eyes and those of most 

 animals. It is quickly bleached by light. It is said to function in nocturnal vision and is 

 abundant in animals that see well at night.) 



It is also interesting to note that the aphakic human eye (eye with lens removed) 

 shows greatly increased sensitivity in the near ultraviolet as compared to a human 

 eye with the lens intact. Although scales used for the curves of Figure 5 do not permit 

 emphasis of this increase, Wald (21) has measured sensitivity increases of as much as 

 1,000 for aphakic eyes. He relates that he has seen 60- and 70-year old aphakics read 

 Snellen charts under conditions where he could not see the chart. Wald accounts for 

 the increased sensitivity to near -ultraviolet by explaining that the lens of the average 

 human eye strongly absorbs (or filters out) wavelengths shorter than about 400 m/i. 

 These wavelengths therefore are not made available to the sensitive visual elements in 

 a normal eye. He goes further to state "it has long been known that certain insects are 

 highly sensitive to ultraviolet light. . . . This need no longer be a matter of speculation 

 for aphakic persons see very well in the ultraviolet". 



The latent capabilities for human vision in the near ultraviolet appear to be further 

 verified by the work of Crescitelli and Dartnell (3), who ran spectral absorption curves 

 on the rhodopsin from recently extracted dark-adapted human eyes. Their work showed 

 strong absorption by rhodopsin of wavelengths in the vicinity of 500 m/i, a decreased 

 absorption at 440 m/i, and maximum absorption at 380 m/l . The work did not include 

 wavelengths shorter than 380 m/i but the shape of the curves indicates a still higher 

 maximum would be reached at 365 m/i. 



Collins and Machado (2) related the response of the codling moth to the motility of 

 the iris -pigment in its compound eyes. In studying its natural behavior the moth was 

 found to be active only during the periods of pigment movement and it would respond 

 to light only when completely or nearly completely dark-adapted. They found that radia- 

 tion in the near ultraviolet region caused the dark-to -light pigment migration to start 

 5 to 10 minutes earlier and proceed to completion 20 minutes sooner than strong light 

 from tungsten lamps and that the speed of pigment migration was related to the bright- 

 ness of the source- -the brighter source being more effective. 



The implications of the foregoing results and comparisons seem to bear out the 

 conclusions of Weiss (23) that "wavelength stimulus possesses both a physical and 

 physiological intensity and that although the physical intensities of wavelengths may 

 be equalized, the physiological intensities produce different effects due to the fact 

 that the absorption of light by the primary photosensitive substance in the visual sense 

 cells varies with wavelength". 



22 



