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.