360 LIGHT AND THE BEHAVIOR OF ORGANISMS 



and some other vertebrates, e.g., the dancing mouse and 

 color-blind persons, is much darker than it is normally 

 for man, and that the visible spectrum for these forms is 

 somewhat shortened at this end. It is evident that the 

 red, which appeared brighter than the blue to the human 

 eye, may have actually appeared darker to the fishes, and 

 if this be true the discrimination may have been made 

 on the basis of brightness. There consequently remains 

 some doubt as to the validity of the conclusion stated 

 above. 



Even in the birds and mammals the question of color 

 vision is not settled, although these animals can undoubt- 

 edly distinguish different regions in the spectrum. But 

 since it is not our object to discuss this subject we shall 

 refer the reader to the excellent researches of Porter (1904, 

 1906) on the birds, Yerkes (1907) on the dancing mouse, 

 Kinnaman (1902) and Watson (1909) on the monkey, and 

 Cole (1907) on the raccoon. 



5. General Summary and Conclnsio?ts of Part IV 



(i) The energy curve in both normal and prismatic 

 spectra is much the same for nearly all sources of light. 

 Beginning with the violet end it rises more or less gradu- 

 ally to a maximum at the red end, 760''^. In the normal 

 or grating spectrum for sunlight, however, the maximum 

 is in the orange at 610"". From this point the energy 

 decreases slightly toward the red end. 



(2) The location in the spectrum of the maximum effect 

 on photochemical reactions depends primarily upon the wave 

 length and the chemical substances which take part in the 

 reaction; and secondarily upon the absorption of light, the 

 distribution of energy and the presence of substances which 

 apparently do not take part directly In the reaction. The 

 reaction between quinine and chromic acid, e.g., takes place 

 most rapidly in the ultra-violet, whereas Triphenylfulgid is 

 changed from the black form to the yellow most rapidly in 



