Histology and embryology / José F. Nonidez.

  • Nonidez, José F. (José Fernandez), 1892-1947.
Date:
1941
Catalogue details

Licence: In copyright

Credit: Histology and embryology / José F. Nonidez. Source: Wellcome Collection.

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    (1) Each chromosome splits lengthwise (if not already split during the prophase). (2) The spindle is now fully constituted. c. Anaphase. The astral fibers attached to the chromosomes seem to contract, pulling the halves of each chromosome toward the poles of the spindle. (1) As a result of the longitudinal splitting of the chromo- somes each daughter cell will receive the same number (48 in man). d. Telophase. This is the final stage of the process during which the daughter groups of chromosomes (now in the poles of the spindle) gradually fade from view as they elongate and lose their compact appearance. (1) A nuclear membrane appears around each group. (2) Division of the cytoplasm takes place at this moment or earlier, in the anaphase. 2. Maturation mitosis. This occurs in the course of the formation of the germ cells in the two sexes. It differs from the somatic in that it separates whole (homologous) chromosomes previously paired during synapsis (see pp. 77, 83). 3. Abnormal mitoses. Irregularities in the process of mitosis are by no means rare, particularly during the formation of the male germ cells. They usually lead to death of the cell. a. Multipolar mitoses, i.e. mitoses in which several spindles are formed, are found in pathological growths such as cancer and tumors. III. Degeneration and Death Cells die in various numbers during the life of the individual without affecting his health. Widespread cell death caused by alter- ations of metabolism, poisons and bacterial toxins, prolonged anae- mia due to thrombosis (infarction), inflammation, hemorrhage, etc., falls within the domain of pathology. Death due to senility of the cells or to physiological changes must be taken into account in histology because degenerating or dead cells can be found in sec- tions of almost any organ. A. Senility. The life span of the cells of the body varies greatly. Some elements as the red blood corpuscles and leucocytes are short- lived and perish daily in large numbers; others seem to live for [4]