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Page:Popular Science Monthly Volume 5.djvu/491

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too small to affect our retina, which will be impressed by the same quantity of pigment when more extended.

It is undoubtedly the nerves which connect the brain with organs where the pigment is retained. By cutting a nerve, the coloring-matter is paralyzed in that portion of the skin through which the nerve passes, just as a muscle is isolated by the section of its nerve. If this operation be performed on a turbot when in a dark state, and thrown into a sandy bottom, the whole body grows paler, excepting the part which cannot receive cerebral influence. The nerves have, in general, a very simple and regular distribution; if two or three of these are cut in the body of the fish, a black transversal band following the course of the nerve will be seen; while, if the nerve which animates the head is thus treated, the turbot, growing paler on the sand, keeps a kind of black mask, which has a very curious effect.

These marks will remain for many weeks, and what may be called paralysis of color has been remarked in consequence of illness or accident. Such was seen in the head of a large turbot, the body being of a different color. It was watched, and died after a few days, evidently of some injury which it had received. The subject offers a field of immense inquiry; the chemical and physical study of pigments, the conditions which regulated their appearance, their intensity, and variations under certain influences; the want of them in albinos, and the exaggerated development in other forms of disease. To Mr. Darwin, and to M. Ponchet, in France, the subject is indebted for much research, which will no doubt be continued as occasion offers.—Chambers's Journal,


By Professor ASA GRAY.

TWO British naturalists, Robert Brown and Charles Darwin, have, more than any others, impressed their influence upon Science in this nineteenth century. Unlike as these men and their works were and are, we may most readily subserve the present purpose in what we are called upon to say of the latter by briefly comparing and contrasting the two.

Robert Brown died sixteen years ago, full of years and scientific honors, and he seems to have finished, several years earlier, all the scientific work that he had undertaken. To the other, Charles Darwin, a fair number of productive years may yet remain, and are earnestly hoped for. Both enjoyed the great advantage of being all their lives long free from any exacting professional duties or cares, and so were able in the main to apply themselves to research without distraction and according to their bent. Both, at the beginning of