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 polynuclcated; 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 met achromatic 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 in 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 becomehypo chromatic, the other hyperchromatic. When this happens the resulting cleavage of the cytoplasm and nucleus is also unequal. Several explanations have been given of 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. Sometimes 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 sarcoma ta 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.
Repair of Injuries
In the process of inflammation we have a series of reactions on the part of the tissues, and fluids of the body, to counteract the ill effects of irritation or injury, to get rid of the cause, and to repair its results. Injury and loss of tissue are usually followed by repair, and both the destructive and reparative changes are, as a rule, classified under the term inflammation. The irritants may be bacteria and their toxins, or they may be mechanical, chemical or thermic.
We do not now concur with the old view that inflammation was essentially an injurious process; rather do we look upon it as beneficial to the organism. In the various reactions of the tissues against the exciting cause of the injury we see a striking example of a beautifully organized plan of attack and defence on the part of the organism.
In some of the infective conditions the conflict fortifies the organism against future attacks of the same nature, as for example in the immunity following many of the acute infective diseases. This acquired immunity is brought about by the development of a protective body as a result of the struggle of the cells and fluids of the body with the invading bacteria and their toxins. This resistance may be more or less permanent. If the invasion is due to a pus-producing micro-organism which settles in some local part of the body, the result is an abscess (fig. 25, Pl. II.).
Abscesses.—One can easily demonstrate all the actions and reactions which take place in this form of acute inflammation. In such a conflict one can see the presence of these minute but dangerous foes in the tissues. At once they proceed to make good their hold on the position they have secured by secreting and throwing out toxins which cause more or less injury to the tissues in their immediate neighbourhood. These micro-organisms having found in the tissues everything favourable for their needs, rapidly multiply and very soon produce serious results. At this point one's attention is focused on the wonderful reactions possessed by the healthy tissues to combat these evil influences.
In a very short period—within three or four hours after infection—there appears to have been a message conveyed to the defenders of the body both as to the point of attack and the nature of the invasion. There is thus brought into play a series of processes on the part of the tissues—the vascular inflammatory changes—which is really the first move to neutralize the malign effects. We find at this early stage oedema of the part. This is an increased exudation of fluid from the engorged blood vessels which not only dilutes the toxins, but is supposed to contain substances which in some way act on these living micro-organisms and render them a more easy prey to the polymorpho-nuclear leukocytes (fig. 23, Pl. II.)—cells that are motile and extremely phagocytic to these bacteria. At this stage the
Fig. 2.—Asymmetrical diaster.
Fig. 3.—Tripolar division in which the splitting of the loops has commenced.
Fig. 4.—Tetrapolar karyokinesis.
Fig. 5.—Another form of tetrapolar division.
Fig. 6.—Cell in a state of degeneration and chromatolysis; the large rounded body in the cell is a cancer parasite.
Fig. 7.—Polynuclcated cell with nuclei of normal size arising from multiple karyokinetic division.
Fig. 8.—Pigmented cell with resting nucleus. The attraction-sphere and centrosome lie in the cytoplasm in the neighbourhood of the nucleus.
Fig. 9.—Hypertrophic nucleolus.
Fig. 10.—Large cell with a single nucleus; nucleoli in a state of degeneration.
Fig. 11.—Multinucleated giant-cell, the nuclei small and produced amitotically.
Fig. 12.—Karyokinetic figure, the one centrosome much larger than the other.
Fig. 13.—Cell in process of karyokinetic division with retention of the nucleolus during the division.
Fig. 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.
Fig. 15.—Division of the nucleolus by elongation, construction, and equilateral division of the nucleus.
Fig. 16.—Division of the nucleolus without any evidence of division of the nucleus.
Fig. 17.—Nucleus with many nucleoli.
Fig. 18.—Direct division of nucleus.
Fig. 19.—Multiple direct division of the nucleus.
Fig. 20.—Nail-like nucleolus.
Fig. 21.—Fragmentation of the nucleus.
