204
H . F I R K E T
reviews are often longer than the present chapter could reasonably be,
so the latter is bound to be very incomplete. Most of the older literature
was reviewed in Hughes' book "The Mitotic Cycle" (1952) and the
very large and recent treatise by Mazia (1961) covers an immense and
varied ground. In this chapter we cannot completely exclude discussion
of various cells whose behaviour may be rather different from that of
animal tissue cells; it would be rather arbitrary to do so. But, in
centering on cultured somatic vertebrate cells, the homogeneity of the
material is increased and the problems may perhaps be better circumscribed. As in all other fields of Cell Biology, the trends have been
towards a more physiological approach and an evaluation of chemical
events. The electron-microscope has made less impact on this than it has
in other chapters of Cytology.
For the first time, the question of the mechanism of mitosis has begun
to emerge from the domain of speculation. The most important point
acquired about cell division in the last decade is that it does not consist
of a rapid duplication of cell elements, but essentially of an equal
separation of parts previously synthesized. Indeed, mitosis could be
said to be mainly movement and catabolism, the necessary anabolic
part of cell multiplication having occurred earlier. This is found to be
true of all parts and constituents of the cell, as technical advances progressively permit their separate study. This justifies the amount of space
devoted in this chapter to events occurring before mitosis.
I I . M I T O S I S
A. G E N E R A L S U R V E Y
1. Definition of Phases
It is not necessary here to give again at length the classical description
of mitosis, familiar to every reader. Observation of living cells by phasecontrast has brought about a habit of subdividing mitosis into 5 phases,
separated by sudden morphological changes—not always so easy to
identify on fixed cells—rather than the old-time 4 stages. It is useful to
determine the overall duration and that of each phase * for each type
of cell used and for each method of culture. This determination is
essential in any study of mitotic poisons which may alter them and it
conditions the relative frequency of phases in fixed and stained preparations. The biochemical events, still largely unexplored, underlying cell
division may not begin and end at the same moments as the morphological phenomena. But the latter furnish us with a convenient time
sequence.
*This already interested W. Fleming in 1882.
H . F I R K E T
reviews are often longer than the present chapter could reasonably be,
so the latter is bound to be very incomplete. Most of the older literature
was reviewed in Hughes' book "The Mitotic Cycle" (1952) and the
very large and recent treatise by Mazia (1961) covers an immense and
varied ground. In this chapter we cannot completely exclude discussion
of various cells whose behaviour may be rather different from that of
animal tissue cells; it would be rather arbitrary to do so. But, in
centering on cultured somatic vertebrate cells, the homogeneity of the
material is increased and the problems may perhaps be better circumscribed. As in all other fields of Cell Biology, the trends have been
towards a more physiological approach and an evaluation of chemical
events. The electron-microscope has made less impact on this than it has
in other chapters of Cytology.
For the first time, the question of the mechanism of mitosis has begun
to emerge from the domain of speculation. The most important point
acquired about cell division in the last decade is that it does not consist
of a rapid duplication of cell elements, but essentially of an equal
separation of parts previously synthesized. Indeed, mitosis could be
said to be mainly movement and catabolism, the necessary anabolic
part of cell multiplication having occurred earlier. This is found to be
true of all parts and constituents of the cell, as technical advances progressively permit their separate study. This justifies the amount of space
devoted in this chapter to events occurring before mitosis.
I I . M I T O S I S
A. G E N E R A L S U R V E Y
1. Definition of Phases
It is not necessary here to give again at length the classical description
of mitosis, familiar to every reader. Observation of living cells by phasecontrast has brought about a habit of subdividing mitosis into 5 phases,
separated by sudden morphological changes—not always so easy to
identify on fixed cells—rather than the old-time 4 stages. It is useful to
determine the overall duration and that of each phase * for each type
of cell used and for each method of culture. This determination is
essential in any study of mitotic poisons which may alter them and it
conditions the relative frequency of phases in fixed and stained preparations. The biochemical events, still largely unexplored, underlying cell
division may not begin and end at the same moments as the morphological phenomena. But the latter furnish us with a convenient time
sequence.
*This already interested W. Fleming in 1882.