Modern surgery, general and operative . brous tissue, fur-nished by the cells of the perichondrium, and the scar is permanent. Cell=division.—The multiplication of connective-tissue cells in repairmay be by direct, but usually is by indirect, cell-di\dsion. Direct cell-divisionconsists in division of the nucleus foUowed by division of the entire cell. Indirect cell-division, or karyokinesis, takes place after remarkable changesin the nucleus. The membrane of the nucleus disappears; the nuclear net-work becomes first close and then more open; and the cell becomes round, ifnot so before. The net
Modern surgery, general and operative . brous tissue, fur-nished by the cells of the perichondrium, and the scar is permanent. Cell=division.—The multiplication of connective-tissue cells in repairmay be by direct, but usually is by indirect, cell-di\dsion. Direct cell-divisionconsists in division of the nucleus foUowed by division of the entire cell. Indirect cell-division, or karyokinesis, takes place after remarkable changesin the nucleus. The membrane of the nucleus disappears; the nuclear net-work becomes first close and then more open; and the cell becomes round, ifnot so before. The network of the nucleus, now consisting of one long fiber,takes the shape of a rosette; next it takes a star form—the aster stage; two Vsnext form—the equatorial stage; an equatorial fine appears and widens,^ andeach one of the Vs retreats toward a pole. Thus two new nuclei areformed, each polar V passing in inverse order through the previous changesof shape, and protoplasm of the original cell collecting about each nucleus(Fig. 67).. Fig. 67.—Forms assumed by a nucleus dividing (Green,from Flemming). Repair of Nerves ^ Repair of Nerves.—A nerve-fiber consists of a core known as the axis-cylinder, which is the essential element in function. About the axis-cyhnderis an-almost liquid material, known as the medullary sheath or white substanceof Schwann, or myelin. The myelin is surrounded by a firm sheath knownas the neurilemma (sheath of Schwann, primitive sheath, neurilemma). Onthe inner surface of the sheath of Schwann, or between it and the white sub-stance of Schwann, are nuclei which are supposed by some to be peripheralnerve-cells (neuroblasts). The neurilemma is absent in the brain and continuity of the white substance of Schwann is interrupted at frequentintervals, and these breaks in the myelin are called nodes of Ranvier. Num-bers of fibers of the kind just described, bound in bundles by connective tissueand surrounded by a fibrous sheath, constitute a
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