CELL, originally a small detached room in a building (Lat cella, a small room), particularly a small monastic house (set ABBEY) . Also used for the small sleeping apartments of the monks or the small dwelling of a hermit. This use still survives in the small separate chambers in a prison (q.v.). The word also denote: various small compartments which build up a compound strut. ture, such as honeycomb, etc.
In electricity a cell may be defined as a system which pro duces electromotive force by chemical action; for voltaic, dry and concentration cells see BATTERY, and ELECTROLYSIS ; Voltaic Cells; for secondary cell see ACCUMULATOR; for gas cell see HYDROGEN ION CONCENTRATION ; for standard cell see INSTRU MENTS, ELECTRICAL.
In biology the term cell denotes microscopic structural elements which form the bulk of the tissues of animals and plants of visible dimensions. The precise meaning of the term cell in bio logical literature is set forth in the article CYTOLOGY (q.v.). When the term came into usage in biology, it referred to the smallest units of structure that the microscope could reveal in the animal or plant body. First used by Robert Hooke (1665) for the minute cavities of cork, a tissue which he described as made up of "little boxes or cells," it is a survival from the microscopic descriptions of plant structure made by 17th century botanists, and as such is really a misnomer, for tissues of animals rarely display the honeycomb-like appearance of pith, cork, etc., when examined microscopically. To-day the cell is recognized to be a complex, consisting of a number of well-defined structures (nucleus, mito chondria, etc.) so that it is no longer possible to define the cell as the ultimate structural unit of living matter. On the other hand, it is a physiological unit. It is the delimitation of this characteristic complex of microscopically visible units by a boundary which possesses the physical property of differential permeability to dif ferent kinds of molecules that characterizes the individual cell, which has thus come to be regarded as a unit of physiological ac tivity of a certain order. The fact that the respective contributions of the maternal and paternal parents to the physical constitution of the offspring are derived in each case from a single cell of the parent-body has revolutionized the study of heredity; and has stimulated a considerable body of research which makes it possible to-day to envisage the structural basis of hereditary transmission and the determination of sex. Thus the Cell Doctrine, i.e., the recognition of the cell originally as the structural unit of the body and later as a unit of physio logical activity, has exerted its influence on every department of biological thought since it was formulated by Schleiden and Schwann in 1839. (L. T. H.)