THE INFLUENCE OF LIGHT ON LIFE. 245 



sort of tinge would remain. From this we may gather that a tem- 

 porary withdrawal of light is not always followed by a loss of the 

 colour-forming power, but that a continued absence of it, as the 

 perpetual darkness of caves, destroys it and bleaches the creatures. 

 It may just be mentioned in passing that it is said that the pigment 

 colours in flowers (not the chlorophyll, of course) can be produced 

 in darkness. 



Now, although we find it stated that darkness does not, imme- 

 diately, hinder the production of colours in animals, yet there can 

 be little doubt that light has an influence, greater or less, in 

 affecting the brilliance or intensity of the colours. That such is 

 the case appears pretty manifest when we contrast the splendid 

 colours of many of the tropical insects and animals with the more 

 sombre hues of the creatures in this part of the world, and 

 remember how much more powerful is the influence of the solar 

 rays in the tropics than it is with us. We seem almost naturally 

 to link the brilliance of tropical light with the brilliance of the 

 plumage of the tropical birds which we are acquainted with on the 

 shelves of museums. If some of these birds, with their rich and 

 gorgeous plumage, be brought to and reared in this country under 

 artificial heat. Dr. Carpenter tells us that they are much longer in 

 attaining their full degree of colour, and that they never exhibit 

 the same amount of brightness as when brought up under the 

 influence of the tropical sun. 



But we do not require to take birds as an example of the 

 variation in colour according to the light, for we only require to 

 compare the skin of any man whom we may find working in the 

 fields beneath the summer's sun with our own skin, and we at once 

 see a very great difference. We know also that a very short expo- 

 sure to the sun is sufficient to spangle the faces of some people 

 with freckles, and that we are not at all surprised when a traveller 

 returns from foreign climes with his complexion changed into a 

 very decided brown hue. 



To refer again to Dr. Carpenter, he says that there can be no 



doubt that the prolonged influence of light, during one generation 



after another, tends to make such a hue permanent. Whether 



this accounts altogether for the black skins of negroes or not, we 



will not stay to consider, as other matters would have to be dealt 



