Sensory Discrimination: Vision 165 



of man. BabSk (11) has studied the effect of different 

 colors on the frog's breathing ; its rate and the movements 

 involved in "throat" and "lung" breathing. The fore- 

 brains of the animals had been removed, a proceeding 

 which makes the breathing of the resting animal more 

 regular. He found that each color produced a breathing 

 curve of a certain specific pattern, and concluded that 

 the colors have specific effects on the eye independent 

 of their intensity. 



The results with turtles, which are reptiles, correspond 

 to those for amphibians, except that Hess (305) finds the 

 spectrum shortened at the violet end ; that is, the turtle 

 does not see beyond the blue. The method used was that 

 of illuminating food with differently colored lights. Hess 

 explains this shortening of the spectrum by the fact that 

 in the turtle eyes, as in those of all birds, a few fishes, and 

 Ornithorhyncus, there are attached to the ends of the 

 cones transparent colored globules like little drops of oil. 

 They are in the turtle mostly red and orange, and would 

 act, Hess thinks, like spectacles of colored glass to cut off 

 the blue and violet rays. The fact that adaptation to 

 darkness apparently occurs in the turtle is of interest 

 because its retina is lacking in rods. The rods, then, can- 

 not be, as they have sometimes been supposed, essential 

 to the process of darkness adaptation. 



§ 43. The Problem of Visual Qualities: Birds 



Many experiments have been made on color discrimina- 

 tion in birds. Most of the older ones were conducted by 

 the method of training the birds to choose between dif- 

 ferently colored papers (611), or between compartments 

 illuminated through differently colored glass (647). These 



