COLOR PHOTOGRAPHY. 173 



adaptation. Thus colors so produced may be called adaptation colors, 

 at the same time remembering that a physical chemical, and in the last 

 analysis a mechanical processes in consideration. An adaptation of 

 such a character may be distinguished as a mechanical adaptation. 



The question arises whether there may not be in nature, rich as it is 

 in color, sensitive substances with the same characteristics as the 

 ground of these photograms. Can not certain adaptation colors in 

 nature be thus explained? To be sure one is accustomed to regard the 

 adaptation in nature in the light of the fundamental law of Darwin of 

 the natural perpetuation by the selection of advantageously altered 

 forms of life. I am not, however, concerned with such a biological 

 adaptation, but only with a mechanical. This conjecture appeared 

 to be confirmed by observations which I found in biological works lent 

 me by the kindness of Professor Oltmanns, of Freiburg. 



I came first of all on the following remark in the work of Theodore 

 Eiiner: "Die Entstehung der Arten auf Grund von Yererben erwor- 

 bener Eigenschaftung nach den Gesetzen organischen Wachsens. 

 Ein Beitrag zur eiuheitlichen Auffassung der Lebewelt." 1 Eimer 

 opposed a too far-reaching estimation of the effect of biological adapta- 

 tion in the agreement of the color of an animal with its surroundings, 

 and pointed out a possible chemical action of light in cases of quick 

 color changes. It has been observed " that butterfly pupae are during 

 their development influenced by the color of their surroundings so far 

 that they assume these colors.' 7 ..." for example the red color of 

 a cloth enveloping them." In explanation of this remarkable observa- 

 tion he assumes that the substance of which the chrysalis is composed 

 "is of such a character that it serves the purpose so ardently sought 

 at present of color photography." 3 In the possibility of such a con- 

 nection I am justified in making mention of this circumstance without 

 having verified the explanation by experiments of my own. It would 

 be scarcely possible for me to add anything new to the excellent, 

 thorough, and protracted experiments which Poulton 3 has carried out 

 on the color adaptation of the caterpillars and their pupae. 



According to these observations, one would not be justified in com-, 

 paring the skin of caterpillars directly wilrh a photographic plate. 

 These are in addition physiological processes. Nevertheless, I will 

 attempt to show from the observations of Poulton that the pigment of 

 the caterpillar's skin during the sensitive states possesses in some 

 degree the peculiarities of a color-receptive substance. 



But if mechanical adaptation occurs in this case, can it not have a 

 more general application in the formation of the living world? I found 

 this supposition confirmed in a paper of August Weisnrann "Aeussere 

 Einflusse als Entwicklungsreize." 4 



1 Eimer 7 Jena, published by Gustav Fischer, 



2 Loc. cit., page 155. 



s Poulton. For the citations, see Chapter XV. 



4 A. Weismaun. Jena. Published by Gustav Fischer, 1894, 



