, _Les
Medailleurs lyonnais_ (Macon, 1897); Dr Julius Cahn, _Medaillen und
Plaketten der Sammlung W.P. Metzler_ (Frankfort-on-Main, 1898);
Molinier, _Les Plaquettes_; I.B. Supino, _Il Medagliere Mediceo nel R.
Museo Nazionale di Firenze_ (Florence, 1899); _L'Arte di Benvenuto
Cellini_ (Florence, 1901); C. von Fabriczy, _Medaillen der
italienischen Renaissance_ (Leipzig); L. Forrer, _Biographical
Dictionary of Medallists, &c._ (London, 1904), &c.
(W. M. R.; E. A. J.)

CELLULOSE, the name given to both an individual--cellulose proper, in
the restricted sense of a chemical individual--and to a group of
substances, the celluloses or cellulose group, which constitute in
infinitely varied forms the containing envelope of the plant cell. They
are complex carbohydrates, or "saccharo-colloids" (Tollens), and are
resolved by ultimate hydrolysis into monoses. The typical cellulose is
represented by the empirical formula C6H10O5, identical with that of
starch, with which it has many chemical analogies as well as
physiological correlations. The representative "cellulose" is the main
constituent of the cotton fibre substance, and is obtainable by treating
the raw fibre with boiling dilute alkalis, followed by chlorine gas or
bromine water, or simply by alkaline oxidants. The cellulose thus
purified is further treated with dilute acids, and then exhaustively
with alcohol and ether. Chemical filter-paper (Swedish) is practically
pure cellulose, the final purification consisting in exhaustive
treatment with hydrofluoric acid to remove silicious inorganic residues.
The "cellulose" group, however, comprises a series of substances which,
while presenting the characters generally similar to those of cotton
cellulose, also exhibit marked divergences. The resemblances are
maintained in their synthetical reactions; but reactions involving the
decomposition of the complex show many variations. For example, cotton
cellulose is difficultly hydrolysed; other celluloses are more or less
readily split up by dilute acids, the extreme members readily yielding
sugars: the hexoses--dextrose, mannose and galactose; and the
pentoses--xylose and arabinose; these less resistant cell-wall
constituents are termed hemi-celluloses.

The celluloses proper are essentially non-nitrogenous, though originating
in the cell protoplasm. The cell-walls of the lower cryptogams, similarly
purified, retain a notable proportion--2.0-4.0%--of con