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Originally appearing in Volume V20, Page 918 of the 1911 Encyclopedia Britannica.
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SERIES OF FIGURES ILLUSTRATIVE OF IRREGULARDIVISION OF CELLS. Figs. 1 to 6 are from the epithelial cells of a cancer of the mamma, (After Galeotti.) 7 to 21 are from a sarcoma. (After Trambusti.) varies in shape, but is usually round or oval, and is sharply defined by a nuclear membrane from the cytoplasm in which it lies. The nucleus in its vegetative stage shows a fine network throughout containing in the meshes the so-called nuclear-sap; attached to the network are the chromosomes, in the form of small irregular masses, which have a strong affinity for the " basic dyes." Embedded in the nucleus are one or more nucleoli (plasmosomes) having an affinity for the " acid dyes." The nucleolus shows an unstainable point at the centre known as the endonucleolus or nucleoluolus (Auerbach). The cell body, or cytoplasm, is apparently composed of a fine reticulum or network, containing within the meshes a soft viscid, transparent substance, the cell-sap, or hyaloplasm, which is probably a nutrient material to the living cell. Within the cytoplasm are found manifestations of functional activity, in the form of digestive vacuoles, granules, fat, glycogen, pigment, and foreign bodies. Usually the cytoplasm shows a marked affinity for the acid stains, but the different bodies found in the cell may show great variation in their staining reactions. The centrosomes which play so important a part in cell division may be found either lying within or at one side of the nucleus in the vegetative condition of the cell. Centrosomes may be single, but usually two are lying close together in the attraction-sphere. When mitosis is about to take place, they separate from one another and pass to the poles of the nucleus, forming the achromatic spindle. After the division and cleavage of the chromosomes of the original nucleus have taken place they pass from the equator to the poles of the spindle, rearranging themselves close to the separated centrosomes to form daughter nuclei. The cytoplasm of the cell now undergoes division in a line between the two daughter nuclei. When complete separation has taken place, we have two daughter cells formed from the original, each being a perfect cell-unit. Some pathological cells, such as the giant-cells of tumours, of bone, and those of tubercle, are polynucleated; in some instances they may contain as many as thirty or more nuclei. The only evidence we have in pathology of living structures in which apparently a differentiation into cell-body and nucleus does not exist, is in the case of bacteria, but then there comes the question whether they may not possess chromatin distributed through their substance, in the form of metachromatic points, as is the case in some infusoria (Trachelocerca, Gruber). Although the methods of cell-division prevailing in normal structures are maintained generally in those which are pathological, yet certain modifications of these methods are more noticeable nn the latter than in the former. Thus in the neoplasmata direct cell-division is more the rule than in healthy parts. In actively growing neoplasmata, certainly, the indirect method prevails largely, but seems to go on side by side with the direct. A curious and interesting modification of the indirect method, known as " asymmetrical division," occurs frequently in epitheliomata, sarcomata, &c. (Hansemann). It consists in an unequal number of chromosomes passing over to each of the daughter nuclei, so that one may become hypochromatic, the other hyperchromatic. When this happens the resulting cleavage of the cytoplasm and nucleus is also unequal. Several explanations have been given of Fig. 2.—Asymmetrical diaster. 3.—Tripolar division in which the splitting of the loops has commenced. 4.—Tetrapolar karyokinesis. 5.—Another form of tetrapolar division. 6.—Cell in a state of degeneration and chromatolysis; the large rounded body in the cell is a cancer parasite. 7.—Polynucleated cell with nuclei of normal size arising from multiple karyokinetic division. „ 8.—Pigmented cell with resting nucleus. The attraction-sphere and centrosome lie in the cytoplasma in the neighbour-hood of the nucleus. 9.—Hypertrophic nucleolus. so.—Large cell with a single nucleus; nucleoli in a state of degeneration. It.—Multinucleated giant-cell, the nuclei small and produced amitotically. „ I2.-Karyokinetic figure, the one centrosome much larger than the other. „ 13.—Cell in process of karyokinetic division with retention of the nucleolus during the division. 14.—Division of the nucleolus and formation of nuclear plate. The nucleolus is elongated, and its longest measurement lies in the direction of the equatorial plane of the nucleus. „ 15.—Division of the nucleolus by elongation, construction, and equilateral division of the nucleus. „ 16.—Division of the nucleolus without any evidence of division of the nucleus. „ 17.—Nucleus with many nucleoli. „ 18.—Direct division of nucleus. 19.—Multiple direct division of the nucleus. „ 2o.—Nail-like nucleolus. „ 21.—Fragmentation of the nucleus.the meaning of these irregularly chromatic cells, but that which most lends itself to the facts of the case seems to be that they represent a'condition of abnormal karyorhexis. In many pathological cells undergoing indirect segmentation, centrosomes appear to be absent, or at any rate do not manifest themselves at the poles of the achromatic spindle. When they are present, that at one end of the spindle may be unusually large, the other of natural size, and they may vary in shape. In pathological cell-division it happens occasionally that the segmentation of the. cytoplasm is delayed beyond that of the mitotic network. The daughter nuclei may have arrived at the anaphase stage, and have even gone the length of forming a nuclear membrane, without an. equatorial depression having shown itself in the cell-body. Some-times the equatorial depression fails entirely, and the separation, as in some vegetable cells, takes place through the construction of a cell-plate. Intranuclear plexuses are not usually found in giant-cells, but have been described in the giant-cells of sarcomata by Klebs and Hansemann, and in those of tubercle by Baumgarten. Some of the nuclei within multinucleated cells may occasionally be engaged in mitotic division, the others being in the resting state. In the earlier accepted notion of direct segmentation, usually known as the schema of Remak, division was described as commencing in the nucleolus, as thereafter spreading to the nucleus, and as ultimately implicating the cell-substance. Trambusti, curiously, finds confirmatory evidence of this in the division of cells in sarcoma. Contrary, however, to the experience of others, he has never found that the attraction-spheres play an important part in direct cell-division, or, indeed, that they exert any influence whatever upon the mechanism of the process. Where pigment was present within the cells (sarcoma), the attraction-spheres were represented by quite clear unpigmented areas, sometimes with a centrosome in their midst.
SERIES (a Latin word from serere, to join)

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