PIGMENT (Lai. pigmentum, from pingerc, to paint; connected with Skt. to adorn). In animals, the coloring granular matter in certain cells of the inner layer ('derma' of vertebrates, 'hypoderma' of arthropods) of the skin. In mammals and man the pigment is brown or near ly black, that of the retina of the eve very black and abundant, and is always situated in cells of the MagpigMarr layer, which lies between the epidermis and derma; in amphibians' the pig ment is accumulated mostly in the derma. partly diffused. and partly inclosed within the cells. In birds, the skin being very thin and eoneealed by the feathers. the coloring matter is mainly eon tined to the feathers. The principal pigments are: Zohne1anin, the black animal coloring mat ter, distributed in antorphons little corpuscles. insoluble in water, alcohol, acid, or ether. lint dissolved and destroyed when boiled in caustic potash and then treated with chlorine; it consists of shout 53.5 per cent. of carbon. 4.6 of hydrogen, 8.2 of nitrogen. and 32.7 of oxygen. Zoaery Orin, red, hitherto found in the red feathers of the cotinga, flamingo, ibis, cockatoo. car dinal-bird. and others, and in the 'rose' around the eyes of the it is soluble in ether. al cohol. and chloroform, but not in acids or in pot ash. Zo?ixantlfin, yellow, can be extracted by boiling in absolute alcohol, and is a diffused pig ment which tinges the shafts. rami, and radii of the feathers. and is possibly the same in the yel low feet and bills of birds of prey and ducks: like zoi)erythrin, it is a colored fatty oil. Turacin is a most peculiar pig-nient. detected in the red feathers of the Musophagida% and scenes to be re stricted to these bird-. It consists of the same elements as zo5melanin with the addition of from 5 to 8 per cent. of copper. Such pigments appear in the coloring matter of birds' eggs. See Ecti.
In inseets the conditions are somewhat dif ferent. as the coloring matter is lodged not only in the scales, but in the skin or crust of the body. The pigment in most insects, as well as in the lobster. is secreted in the deeper layer of the skin, under the cuticle. and this layer is called the hypodermis. When the lobster casts its shell the soft hypodermal layer consists of cells which are tilled with red and blue pigment masses. This cellular layer gives rise to the outer cuticle, which thus derives its hue, red and blue, from the deeper inner layer of color-seereting In most insects the cuticle is nearly colorless, or horn-colored or honey-yellowish. in tint.
It has been found by experiments that pig ments may he dissolved out by chemical reagents and subsequently restored by other agents. Both
Coste and Creek have proved that red, yellow. brown. and black colors in the scales of certain butterflies are always due to pigments, and in a few eases greens, blues, violets, purples. and whites are due to the presence of pigments in the scales themselves. Dr. A. 0. Mayer believes that the pigments of lepidopterous insects are derived from the blood of the chrysalis. The first color to appear in the pupa or chrysalis of the Ameri can silkworm. on which he made his observations, is (lull yellow sloe or drab: this is of the hue of the blood when removed from the chrysalis and exposed to the air. Mayer has also artificially produced several kinds of pigments from the blood. which are similar in color to various markings on the wings of the imago. or adult. Ile has also found that chemical reagents have the same effects on these manufactured products as on similar pigments in the wings of the liv ing moth.
As regards pigmental colors. Baer classified them into two types: diffused and granular. Pigments. of the first type are diffused through the chitin or substance of the scale, are usually present in very small amount, and include the dark pigments. most yellows, oranges, and reds, except in the Pierida., and the whites (uric acid) of the Pieriikr. later also, contrary to the results of Hopkins, found that some of the orange and yellow pigments of the Pierida• are diffuse and not granular. Granular pigments occur exclu sively in the Pierid:e and are yellow or red in color. They color the scales in which they occur very deeply. Such scales are few' in number and almost without surface sculpturing. The super position of dark-colored scales upon scales deeply tinted by yellow granular pigment may. as in Anthorhous eardamines, produce a greenish tint.
Equal activity has been shown by chemico biologists in the study of the coloring matter of flowers. It is now held that nearly all blue and red pigments originate from tannin; in other words, tannin constitutes the ehromogen of the red and blue floral pigments. Keegan showed that the circumstances which created or influ enced the particular tint of dowers was first ehemieal (the presence of quereetin in the form of rutin, etc.. h: the corolla ), and seeond, physio logical. i.e. the possession by the corolla of en ergetic respiratory and transpiratory functions, with the result that the substances contained in its cells underwent an oxidation more or less vigorous and complete.