The Ethics of Medical Homicide and Mutilation

by Austin O'Malley

Fig. II

Diagram of Mitosis.

1. Cell with resting Nucleus. 2. Prophase: Chromatin in thickened convoluted threads, beginning of Spindle. 3. Prophase: Chromosomes. 4. Prophase: Spindle in long axis of the Nucleus, Chromosomes dividing. 5. Anaphase: Chromosomes moving toward the Centrosomes. 6. Chromosomes at the poles forming the Diaster, beginning splitting of the Cell-body. 7. Telophase, Daughter-Nuclei returning to resting state. 8. Daughter-Nuclei showing Monaster below. 9. The two new Cells.

It is almost an established fact that each species of animal and plant has a fixed and characteristic number of chromosomes, which regularly recurs in the division of all its cells. In forms arising by sexual production the number is even. The number of chromosomes in the human cell is said to be forty-eight. There are, according to some observers, forty-seven chromosomes in man and forty-eight in woman. There seem to be twice as many chromosomes in white men as in negroes. Wilson gives the number[30] of specific chromosomes for seventy-four animals and plants. Germ-cells as differentiated from the somatic cells have in the perfected cell always half the number of chromosomes found in a somatic cell.

While these changes are going on in the chromatin the Amphiaster forms. This consists of a fibrous spindle-shaped body, the Spindle, at either pole of which is an Aster made up of rays. In the centre of each aster is a Centrosome, and this may have a Centrosphere about it. As the amphiaster grows the centrosomes are grouped in a plane at the equator of the spindle, forming the Equatorial Plate. (Fig. II, No. 4.) The process so far makes up the Prophases of the Mitosis.

In the Metaphases of the Karyokinesis begins the actual division of the cell. Each chromosome splits lengthwise into exactly similar halves, and these, in the Anaphases of the mitosis, drift out to the opposite poles of the spindle to form the daughter-nuclei of the new cells. The daughter-nuclei receive precisely equivalent portions of chromatin from the mother-nucleus, and this is an important fact in mitosis. As the chromosomes go toward the poles the cell-body begins to constrict at the equator.

In the final phases, the Telophases, the cell divides in a plane passing through the equator of the spindle, and each daughter-cell receives half the chromosomes, half the spindle, and one of the asters with its centrosome. A daughter-nucleus is reconstructed in each cell from the chromosomes. The aster commonly disappears and the centrosome persists, usually outside the new nucleus, but sometimes within it. Every phase of mitosis is subject to variation in different kinds of cells, but the outline of the division given here is the fundamental method.

The germ-cells differ from the body-cells in general by containing half the number of chromosomes characteristic of a given animal or plant. If the body-cell has, say, twenty-four chromosomes, the spermatozoön of the animal or plant from which the cells are taken will have twelve chromosomes and the ovum will have twelve. When the nuclei of these two cells unite in fertilization the resulting primordial cell will have the twenty-four chromosomes restored, the specific number for this plant or animal. In oögenesis and spermatogenesis the phases of "Reduction," wherein the ovum and spermatozoön get rid of half the chromosomes during the stages of maturation of these germ-cells, are somewhat similar for both sexes. The process is very complicated, but it is of importance in the theories of inheritance. All the physical characteristics in a human being that come to him from his parents and remoter ancestors are supposed, by the biologists, to reach him through the chromosomes in the nuclei of the single parental germ-cells. The maternal physical heredity is handed on through the chromosomes in the ovum. The fetus in the womb is a parasite, autocentric, feeding at the start from the deutoplasm, or yolk, in the ovum, and later from the supplies brought to it by the maternal blood. The physical material it gets directly from the mother is very probably all in the chromosomes of the fecundated ovum. Some weeks elapse, and the embryo is quite advanced before it begins to draw food from the mother at all. So far as the father is concerned, there is no doubt whatever that every physical and pathological characteristic that can be handed down—and there are many such qualities—must come through the chromosomes of the paternal spermatozoön. Certain physical characteristics are passed on for centuries in a family—the Norseman's body in northeastern Ireland, the skin-pigment in the American negro, and so on indefinitely—and these qualities cannot come down except through the chromosomes. The germ-plasm has come to us from the first man, and it will be passed on to the last person of the race—we are all literally uterine brothers.

In the reduction of the germ-cells, if the primordial cell that finally produces the ovum has, say, four chromosomes, these four chromosomes first split longitudinally and reduce into two tetrads, or two groups of four chromosomes. Outside the nucleus is a spindle toward which the two tetrads move; they pass out of the nucleus and become the equatorial plane of the spindle; each tetrad divides into dyads (pairs of chromosomes), and one pair of these dyads remains in the ovum, while the other pair leaves the ovum entirely and becomes the nucleus of an abortive cell, called the First Polar Body. Later a second polar body forms and carries another dyad (two chromosomes) out of the ovum, leaving only one dyad, or two chromosomes, in the germ-cells; that is, half the number of chromosomes that were in the primordial cell.

The reduction-division in spermatozoa is similar, but the end process leaves four active spermatozoa, whereas in the ovum the final result is one ovum and three practically inert and cast-off polar bodies. The reduction-division in both ovum and spermatozoön is in reality far more complicated than the broad summary given here. In parthenogenetic insects and animals a polar body takes the place of the spermatozoön, and fuses with the egg-nucleus to start mitosis.