CHEMICAL NATURE OF COLOR 



acids or alkalis under the influence of air, light, and heat. He con- 

 cludes : 



1. That some colors of insects can be changed or obliterated by 

 acids. 



2. That two natural colors, madder-lake and indigo, can be pro- 

 duced artificially by the influence of acid on fat-bodies. 



3. As protein bodies in insects are changed into fat-bodies, and 

 may be changed by acids contained in insects into fat-acids, the for- 

 mation of colors in the same manner seems probable. 



4. That colors can be changed by different temperatures. 



5. That the pattern is originated probably by a combination of 

 oxygen with the integument. 



6. That mimicry of the hypodermal colors may be effected by a 

 kind of photographic process. 



7. Finally, color and pattern are produced by physiological pro- 

 cesses in the interior of the bodies of insects. 



Krukenberg concludes that change of color (in perfectly developed insects) 

 is a consequence of the change of food, and can be explained by the alteration 

 of the pigment through heat and light. His experiments were made in order 

 to ascertain the cause of the turning of green grasshoppers in autumn into yel- 

 low and pink. He tried to answer two questions : First, does the pigment of 

 grasshoppers originate directly out of the food, and does it consist of pure 

 chlorophyll or of a substance containing chlorophyll, or is it to be accepted as 

 a peculiar product of the organism ? Second, is the color the consequence of 

 only one pigment, or of several ? Special analysis proves that the green color 

 has no connection with chlorophyll. He concludes: "It is evident that the 

 green color of the grasshopper is the consequence of several different pigments 

 which can be separated by a chemical process." Krukenberg believes that light 

 has a marked influence on the color of insects and that light turns to red or 

 pink the insects which were green during the summer. It would seem, how- 

 ever, more probable that cold was the agent, the change being due to the colder 

 autumn weather. 



Here we might refer to the results of the studies of Buckton and Sorby, on 

 the changes in color of Aphides : 



" 1. The purple coloring matter appears to be a quasi-living principle, and 

 not a product of a subsequent chemical oxidizing process. Mounted in balsam 

 or other preserving fluids, the darker species stain the fluid a fine violet. 



"2. As autumn approaches and cold weather reduces the activity of the 

 Aphides, the lively greens and yellows commonly become converted into ferru- 

 ginous red, and even dark brown, which last hue in reality partakes more or less 

 of intense violet or purple. These changes have some analogy with the brilliant 

 hues assumed by maple and other leaves during the process of slow decay. 



"3. Aqueous solutions of crushed dark brown and yellow-green varieties of 

 Aphides originate different colors with acids and alkalies. 



"4. In the generality of cases coloring-matters, such as indigo, Indian yel- 

 low, madder-lake, and the like, do not separately exist in the substance of vege- 

 tables, but the pigments are disengaged through fermentation or oxygenation. 

 Again, alizarin itself is reddish yellow, but alkaline solutions strike it a rich 



