242 Chromatic Adaptation. 
chromatic adaptation, for chlorophyll itself is apparently essentially 
the same substance throughout the whole range of C0. 2 -assimilating 
plants. 
This experimental production of complementary chromatic 
adaptation takes rank as a quite new phenomenon, both from a 
physical and from a biological point of view. The production of 
the converse phenomenon, “ sympathetic chromatic adaptation ” is 
however known physically in a few cases and has often been 
observed biologically in such cases as the “ protective colouration ” 
of insects. 
In the latter we find the insect developing a pigment of the 
same colour as the light which is shining on it from its enviroment, 
while of the former we have a very good example when a surface of 
mixed chlorides of silver and other metals, illuminated by a 
spectrum, gives an image of the spectrum in approximately the 
true colours in all its parts. This phenomenon, extraordinary as it 
appears at first sight, has been satisfactorily explained by Wiener. 1 
It is due to the salts being sensitive to all wave-lengths of light 
and giving with white light an appearance of darkening due to a 
mixture of all possible coloured particles. When now the red of 
the spectrum shines on this it slowly decomposes all the particles 
that absorb the red rays. The only particles of the mixture that 
will not absorb red light are of course the red particles and these 
alone remain and give a red patch of pigment. So in the blue part 
of the spectrum all the particles except the blue are decomposed 
and a blue patch results: similarly with intermediate parts of the 
spectrum. 
The colouration changes studied by Keeble and Gamble 3 in 
Hippolyte varians seem to be quite different and much more complex. 
These reactions of chlorides may throw light on sympathetic 
chromatic adaptation but it is not clear how they help the case 
of complementary chromatic adaptation. This latter is not a 
direct complementary reaction of the coloured cell to the new 
coloured light as is indicated by the long series of colour stages that 
must be gone through before the final complementary colour is 
arrived at. 
It is to be hoped that investigation may soon bring us a fuller 
comprehension of this new and important chromatic adaptation. 
1 Wiener. Farbenphotographie, Annalen d. Physik. u. Chernie, 
Bd. 55, 1895. 
2 Keeble & Gamble. Quart. Journ. Mic. Sci., Vol. 43 ; also Phil. 
Trans., Royal Society, Vol. 196, 13. 
