The Eye and the Spectrum 



Since near-infrared radiation may then 

 be expected to penetrate the water suff ici - 

 ently to be of use, it is pertinent to consid- 

 er the relation of the spectrum to the 

 vertebrate eye, with respect to a possible 

 influence on behavior . The rods of the 

 vertebrate eye furnish the hazy, black-and- 

 white percepts of dim light, and the cones 

 give the sharp, colored images of bright 

 light. The rods are greatly aided in their 

 scotopic (dark -adapted) function b> the pig- 

 ment rhodopsin, which in turn limits the 

 spectral sensitivity of the rods to 650 m . , at 

 which wavelength rhodopsin becomes color- 

 less and loses its photosensitivity. The 

 cones alone perceive wavelengths greater 

 than 650 m . , and see them as red light. 

 Walls (1942) notes that fish rhodopsin "in its 

 shortening at the red end and in the position 

 of its maximum is clearly adjusted to the 

 kind of light in which it is to operate. It is 

 thus no mere coincidence that the visible 

 spectrum is roughly the transmission spec - 

 trum of water ." 



The ability to discriminate hue does not 

 necessarily imply that the visible spectrum 

 is thereby extended. Wails reviewed the 

 color-vision work with fishes and other verte- 

 brates done before 1942, and suggests a 

 method (p. 471) whereby the limit of an ani- 

 mal's spectrum may be determined: "By 

 training to darkness versus a red wavelength, 

 and increasing that wavelength slowly, the 

 limit of the animal's spectrum can be found 

 at that wavelength which, however intense 

 physically, is invisible- -at the border of 

 (the animal's) infrared." Subsequent work 

 has been done on the light reactions of 

 fishes, but radiations used have not extended 

 into the infrared wavelengths. 



Infrared Radiation and Animals Other Than 

 Fishes. 



In lieu of data on the reaction of fishes 

 to infrared radiation it may be well to con- 



sider the reactions of other animals in 

 that regard. Luckiesh and Moss (1936) 

 found with respect to the human eye that 

 "infrared radiation apparently has no 

 specific action upon t±ie tissues analogous 

 to that of abiotic or ultra-violet radiation." 



Vanderplank (1934) reported that the 

 tawny owl (Strix aluco) was able to find 

 living animals in total darkness by the 

 longwave infrared radiation from the body 

 of the prey, and that the pupil of the owl's 

 eye was contracted by hot -body mfrared 

 radiation. Matthews and Matthews (1949), 

 working with the same species of owl and 

 like radiation, found that an oscillograph 

 and amplifying system could not detect a 

 retinal potential and that any transmission 

 through an extirpated eye was too small to 

 measure with a thermopile. Hecht and 

 Pirenne (1940) found that "infrared radia- 

 tion (750-1500 m.) produces no iris 

 contraction in the typically nocturnal long- 

 eared owl." Dice (1945) studied four 

 species of owls and discovered no evidence 

 that they could utilize infrared radiation to 

 find their prey . 



Gunter (1951) employed both the dis- 

 crimination method involving trained 

 animals and the pupillo -motor response 

 criterion in working with cats . He reports 

 that the animals could not discriminate 

 between darkness and infrared radiation, 

 and that a pupillo -motor response was not 

 observed when the dark-adapted cat's eye 

 was directly stimulated with infrared 

 radiations. 



Vision in the infrared spectrum has 

 been claimed for three species of water 

 tortoises (Wojtusiak, 1949; Wojtusiak and 

 Mlynarski, 1949). It should be noted that 

 the filters used passed wavelengths of from 

 700 to 750 m . , which are considered within 

 the red range of the visible spectrum. 



Southern, Watson, and Chitty (1946) 

 used an infrared sensitive telescope with 



