COLOR PHOTOGRAPHY. 205 



This possibility and the recognition of its cause form a new basis for 

 a kind of color photography which may be distinguished as body color 

 photography. The hope seems justified that upon this foundation 

 there may be built up new processes superior to the old body-color 

 processes in accuracy and fixedness of the pictures. 



Color reproduction can be designated as color adaptation, for it con- 

 sists in the perpetuity of color substances which best withstand the 

 action of colored illumination — that is, of similarly colored substances. 



This circumstance raises the question whether color adaptation can 

 be produced in a similar way in nature, that is through a process of 

 mechanical adaptation in contradistinction to biological adaptation, 

 which according to Darwin results by natural selection of individuals. 



Such a case is presented by the caterpillars and their pupre and has 

 been thoroughly investigated by Poulton. While his experiments show 

 the presence of complicated physiological processes, yet they make the 

 assumption plausible that the coloring matter of these animals within 

 the sensitive stages of development possesses to a certain degree the 

 characteristics of a color-receptive substance. 



In this case the phenomenon would belong to a general group of 

 phenomena discovered by Wilhelm Eoux and classed under the title 

 of functional adaptation. 



I believe that with the above the work of the physicist in connection 

 with mechanical color adaptation is chiefly finished, and it is now the 

 function of the chemist and photographer, on the one hand, and of the 

 biologist, on the other, to make the physical results practically useful. 



Phys. Inst. d. Techn. Hochschule Aachen, April 25, 1895. 



