Underneath the colour-bags (or chromoblasts as they are called) of Milne-Edwards, Pouchet, a recent inquirer, has discovered a remarkable layer, which he calls cærulescent, and which possesses the singular property of appearing yellow on a clear, and blue on an opaque background.
M. Paul Bert, within the last two years, has by his researches thrown still further light upon these curious changes, and upon the mechanism by which they appear to be accomplished. He endorses most of the results of Milne-Edwards and subsequent inquirers, but has carried his observations much further. It would be out of place here to give a detailed account of the methods by which M. Bert has arrived at his conclusions. Suffice it to say, that by a series of careful experiments, he has discovered that these changes of colour seem to be entirely under the control of the nervous system, and that the chameleon can no more help them taking place than a toad can help twitching its leg when pinched. By acting in various ways upon the spinal marrow and the brain, the operator can send the colour to or withdraw it from any part of the body he pleases. Indeed a previous observer was able to cause a change of colour in a piece of the skin of the animal by acting upon it with electricity; and M. Bert has proved that even in the absence of the brain the usual changes can be produced by exciting the animal in any way; thus shewing that they are due to that class of nervous action which physiologists name reflex, and of which sneezing is a good example. M. Bert has also made some interesting experiments on the animal while under the influence of anæsthetics and during sleep. It was formerly known that in the latter case, and also after death, the chameleon assumed a yellowish colour, which under the influence of light became more or less dark. M. Bert has found that exactly the same effects are produced during anæsthesia as during natural sleep, and that light influences not only dead and sleeping chameleons, but that it modifies in a very curious fashion the coloration of the animal when wide awake. The same result is produced when the light is transmitted through glass of a deep blue colour, but ceases completely when red or yellow glass is used. To render these results more decisive, M. Bert contrived to throw the light of a powerful lamp upon a sleeping chameleon, taking care to keep in the shade a part of the animal's back, by means of a perforated screen. The result was curious: the head, the neck, the legs, the abdomen, and the tail became of a very dark green; while the back appeared as if covered with a light brown saddle of irregular outline, with two brown spots corresponding to the holes in the screen. Again, by placing another animal, quite awake, in full sunlight, but with the fore-part of its body behind a piece of red glass, and the hind-part underneath blue glass, M. Bert divided the body into two quite distinct parts—one of a clear green with a few reddish spots, and the other of a dark green with very prominent spots.
From his researches as a whole, M. Bert concludes: 1. The colours and the various tints which chameleons assume are due to changes in the position of the coloured corpuscles, which sometimes, by sinking underneath the skin, form an opaque background underneath the cærulescent layer of Pouchet; sometimes, by spreading themselves out in superficial ramifications, leave to the skin its yellow colour, or make it appear green and black. 2. The movements of these colour-bags or chromoblasts are regulated by two groups of nerves, one of which causes them to rise from below to the surface, while the other produces the opposite effect.
As to the effects produced by coloured glass, they no doubt result from the fact that the coloured corpuscles, like certain chemical substances, are not equally influenced by all the rays of the spectrum, the rays belonging to the violet part having alone the power of causing the colour-bags to move and drawing them close to the surface of the skin. This exciting action of light on a surface capable of contraction, an action which hitherto has only been recognised in the case of heat and electricity, is one of the most unexpected and curious facts which in recent times have transpired in the domain of physiology. Hence M. Paul Bert's researches are likely to prove of far more value than merely to explain the changes of colour which take place in the chameleon. He hopes especially in carrying out his researches to discover the reason of the favourable influence on health which is exerted by the direct action of light on the skin of children and of persons of a lymphatic temperament; and this may lead to some very important practical results in the treatment of disease. In the meantime he has done much to clear up a very puzzling and very interesting fact.
[MY SWEETHEART.]
Do you know my sweetheart, sir?
She has fled and gone away.
I've lost my love; pray tell to me
Have you seen her pass to-day?
Dewy bluebells are her eyes;
Golden corn her waving hair;
Her cheeks are of the sweet blush-roses:
Have you seen this maiden fair?
White lilies are her neck, sir;
And her breath the eglantine;
Her rosy lips the red carnations:
Such is she, this maiden mine.
The light wind is her laughter;
The murmuring brooks her song;
Her tears, so full of tender pity,
In the clouds are borne along.