COLOR PHOTOGRAPHY. 201 



The relation sought is probably the ineffectiveness of light when 

 reflected and its activity when absorbed, so far as color adaptation is 

 concerned, which depend on whether it agrees in color with the sub- 

 stance on which it falls or not. 



In order to show that the remarkable influencing of the condition 

 of the future skin and the effect of the illumination of a part of the 

 skin are not in contradiction to this supposition, I must remark that 

 processes are conceivable which are set up in connection with the 

 commencement of the light absorption. 



Poulton thought it possible that the surface colored layer is in a 

 state of "complete physiological unity," 1 and that the nerve system 

 conducted the light action. It is not difficult to build up from this an 

 accurate physical conception. I recall phenomena which Ostwald 2 has 

 classed under the name of chemical actions at a distance. Amalga- 

 mated zinc can be dissolved by dilute acids acting not directly on the 

 zinc but on a platinum wire which is placed in metallic contact with 

 the zinc, but when the zinc and platinum are separated by a clay cell 

 and the former dipped in a neutral solution. This action is, of course, 

 by means of an electrical current. 



In a similar way the illumination of the coloring matter of a cell may 

 set up electrical currents in the nerve conductors which cause similar 

 decomposition in other cells of the caterpillar's skin, such action being 

 accompanied, of course, by a diminution of intensity of action in the 

 exposed cells. In this way there would be caused a uniform change 

 over the whole body. Such a transference of action may be compared 

 with an apparatus to see things occurring at a distance or an arrange- 

 ment to electrically photograph objects far removed. 



Since, according to Poulton, not only the illuminated skin, but the 

 colorless skin lying beneath it, is influenced, it must be assumed that 

 in some way the decomposition is transferred to this latter, with the 

 result of reversing the effect in the outer skin. This decomposition 

 must hinder the later formation of coloring matter. Such peculiar con- 

 ceptions are, to be sure, as yet premature, and are only made to show 

 that the relation to color photography is not excluded. They are 

 indeed complicated, but so is the process itself. Since nature proceeds 

 from the simple to the complex it would be remarkable if cases should 

 not yet be found in which the process remained at a less advanced 

 stage of development and thus showed a direct relation to color 

 photography. 



Poulton 3 refers to similar processes the capacity of Halias prasinana 

 to spin a cocoon agreeing in color with its surroundings. 



The transferrence to a distance in caterpillars explains also the 

 activity where dark surroundings are adjacent to light, for the parts 



Poulton. Trans. Ent. Soc, page 392. 1892. 



* Ostwald. Zeits. fur Phys. Chem., 9: page 540. 1892. 



3 Poulton. Trans. Ent. Soc, page 392, 1892; Colours of Animals, page 145. 



