In Biology, the word “cell” denotes the fundamental form-element of
every organized body. It is a bioplastic mass of protoplasm, varying
in size and shape, generally of microscopic dimensions, capable, under
proper conditions, of performing the functions of sensation, nutrition,
reproduction and automatic or spontaneous motion, and constituting
in itself an entire organism, or being capable of entering into the
structure of one.
Such a cell, as a rule, has a nucleus and is usually also provided with
a wall or definite boundary; but neither cell-nucleus nor cell-wall
necessarily enters into its structure. In ultimate morphological
analysis, all organized tissue is resolvable into cells or cell
products. See “Protoplasm,” and “Cell Theory,” infra.
Specifically, the word “cell” denotes a nucleated capsulated
form-element of any structure or tissue one of the independent
protoplasmic bodies which build up an animal fabric. A body consisting
of cell substances, cell-wall and cell-nucleus, as bone cells,
cartilage-cells, muscle-cells, nerve-cells, fat-cells, cells of
connective tissue, of mucous and serous membrane, etc., of the blood,
lymph, etc. This is the usual character of cells in animals, and is the
ordinary technical anatomical sense of the word.
“However complicated one of the higher animals or plants may be,” says
Huxley, “it begins its separate existence under the form of a nucleated
cell.”--Huxley, _Anatomy Invert. An. p. 19_.
See Haeckel, Ev. Man, chap. 6. “_Ovum and amœba_,” pp. 36-50; Spencer,
_Principles, Biology, Index, “Cell,”_ 2 p. 630; Romanes, _Darwin,
etc._, 1, pp. 104-134; _Encyc. Brit. 12_, pp. 5-10, “_Histology_;”
_New Int. Encyc. 4_, p. 400.
Professor McMurrich, of the University of Michigan, says:
“It has been estimated that the number of cells entering into the
composition of the body of an adult human being is about twenty-six
million five hundred thousand million.” (McMurrich, _Development, Human
Body_, p. 18.) This number is equivalent to twenty-six and a half
trillions.
The “cell theory” is the doctrine that the bodies of all animals and
plants consist, either of a cell, or of a number of cells, and their
products; and that all cells proceed from cells, as expressed in the
phrase _omnis cellula e cellula_: a doctrine foreshadowed by Kasper
Freidrich Wolff, who died in 1794, and by Karl Ernst Von Baer (born
1792.) It was established in botany by Schleiden in 1838, and in
zoology by Theodor Schwann about 1839.
Its complete form, including the ovum, as a simple cell, also, is the
basis of the present state of the biological sciences.--_Cent. Dic. 1,
p. 879, col. 1._