5. T H E L O C O M O T O R Y B E H A V I O U R OF CELLS
191
probable it was that Ingvar had inadvertently introduced contactguidance into his cultures, and influenced his cells in this way. Peterfi
and Williams (1934) observed immediate changes of cell form, oriented
in relation to a current, which could be an incipient polarization of
movement. The most important positive results have been obtained by
Marsh and Beams (1946). They applied direct current, throughout the
period of culture, to nerve fibres growing from explants of chick brain.
They found that above a threshold current density (many times higher
than that used by Ingvar) nerve fibres failed to emerge on the anodal
side of the explant; and wherever else they grew out, most of them were
oriented in the direction of the cathode. The effects could be modified
according to expectation by rotating the culture through 90° in the
middle of the period of exposure to the current; the authors point out
that this makes it difficult to suppose that the orientation of the cells is
mediated via orientation of the fibrin, which is not likely to be so
easily altered.
E. S T A R T I N G A N D S T O P P I N G
It is convenient to treat the starting and stopping of cells separately
from the kineses and taxes. A cell may stop moving because of an
extreme expression of a behaviour reaction which is either oriented or
unoriented. For instance, a cell may stop if a stimulus which slows it is
applied in extreme degree; or if a stimulus which makes it move away
(such as contact inhibition) is applied from all directions. Similar considerations apply to starting.
Problems of starting and stopping are of importance in vivo. The cell
movement in vivo that characterizes early embryonic development
gradually comes, if not to a standstill, at least to be little more than
oscillation round a median position. The power of stopping in the right
place is indeed well developed in embryonic cells, as demonstrated by
the sorting out according to cell type found in disaggregated embryonic
tissues (Moscona and Moscona, 1952) or the specific connexions made
by neurite terminations. Cell movement is, however, readily reawakened by injury or other stimulus to the local formation of new
tissue; and in malignancy it is pathologically reawakened.
Trapping by directional reactions occurs when a cell is confined to a
small region by some surrounding discontinuity or very short gradient
at which a negative taxis occurs. Within the confines of the region, if it
is large enough, the cell is free to oscillate. A fibroblast is trapped in
this way when it lies in the middle of a confluent monolayer of other
fibroblasts which is showing no general trend of motion. Contact
inhibition then operates in all directions (Abercrombie and Heaysman,
191
probable it was that Ingvar had inadvertently introduced contactguidance into his cultures, and influenced his cells in this way. Peterfi
and Williams (1934) observed immediate changes of cell form, oriented
in relation to a current, which could be an incipient polarization of
movement. The most important positive results have been obtained by
Marsh and Beams (1946). They applied direct current, throughout the
period of culture, to nerve fibres growing from explants of chick brain.
They found that above a threshold current density (many times higher
than that used by Ingvar) nerve fibres failed to emerge on the anodal
side of the explant; and wherever else they grew out, most of them were
oriented in the direction of the cathode. The effects could be modified
according to expectation by rotating the culture through 90° in the
middle of the period of exposure to the current; the authors point out
that this makes it difficult to suppose that the orientation of the cells is
mediated via orientation of the fibrin, which is not likely to be so
easily altered.
E. S T A R T I N G A N D S T O P P I N G
It is convenient to treat the starting and stopping of cells separately
from the kineses and taxes. A cell may stop moving because of an
extreme expression of a behaviour reaction which is either oriented or
unoriented. For instance, a cell may stop if a stimulus which slows it is
applied in extreme degree; or if a stimulus which makes it move away
(such as contact inhibition) is applied from all directions. Similar considerations apply to starting.
Problems of starting and stopping are of importance in vivo. The cell
movement in vivo that characterizes early embryonic development
gradually comes, if not to a standstill, at least to be little more than
oscillation round a median position. The power of stopping in the right
place is indeed well developed in embryonic cells, as demonstrated by
the sorting out according to cell type found in disaggregated embryonic
tissues (Moscona and Moscona, 1952) or the specific connexions made
by neurite terminations. Cell movement is, however, readily reawakened by injury or other stimulus to the local formation of new
tissue; and in malignancy it is pathologically reawakened.
Trapping by directional reactions occurs when a cell is confined to a
small region by some surrounding discontinuity or very short gradient
at which a negative taxis occurs. Within the confines of the region, if it
is large enough, the cell is free to oscillate. A fibroblast is trapped in
this way when it lies in the middle of a confluent monolayer of other
fibroblasts which is showing no general trend of motion. Contact
inhibition then operates in all directions (Abercrombie and Heaysman,