t similar pigment
has been noticed. Other pigments have been described, such as
actiniochrome, echinochrome, pentacrinin, antedonin, polyperythrin
(which appears to be a haematoporphyrin), the floridines,
spongioporphyrin, &c., which need no mention here; all these pigments
can only be distinguished by means of the spectroscope.

Most of the pigments are preceded by colourless substances known as
"chromogens," which by the action of the oxygen of the air and by other
agencies become changed into the corresponding pigments. In some cases
the pigments are built up in the tissues of an animal, in others they
appear to be derived more or less directly from the food. Derivatives of
chlorophyll and lipochromes especially, seem to be taken up from the
intestine, probably by the agency of leucocytes, in which they may occur
in combination with, or dissolved by, fatty matters and excreted by the
integument. In worms especially, the skin seems to excrete many effete
substances, pigments included. No direct connexion has been traced
between the chlorophyll eaten with the food and the haemoglobin of blood
and muscle. Attention may, however, be drawn to the work of Dr E.
Schunck, who has shown that a substance closely resembling
haematoporphyrin can be prepared from chlorophyll; this is known as
phylloporphyrin. Not only does the _visible_ spectrum of this substance
resemble that of haematoporphyrin, but the _invisible_ ultra-violet
also, as shown by C. A. Schunck.

The reader may refer to E. A. Schafer's _Text-Book of Physiology_
(1898) for A. Gamgee's article "On Haemoglobin, and its Compounds"; to
the writer's papers in the _Phil. Trans._ and _Proc. Roy. Soc._ from
1881 onwards, and also _Quart. Journ. Micros. Science_ and _Journ. of
Physiol._; to C. F. W. Krukenberg's _Vergleichende physiologische
Studien_ from 1879 onwards, and to his _Vortrage_. Miss M. I. Newbigin
collected in _Colour in Nature_ (1898) most of the recent literature
of this subject. Dr E. Schunck's papers will be found under the
heading "Contribution to the Chemistry of Chlorophyll" in _Proc. Roy.
Soc._ from 1885 onwards; and Mr C. A. Schunck's paper in _Proc. Roy.
Soc._ vol. lxiii. (C. A. MacM.)

COLSTON, EDWARD (1636-1721), English philanthropist, the son of William
Colston, a Bristol merchant of good position, was born at Bristol on the
2nd of November 1636. He is generally understood to have spent some
years of his youth