5 . T H E L O C O M O T O R Y B E H A V I O U R OF C E L L S
183
O f the factors influencing speed of movement, we may consider first
diffusible substances in the liquid medium. There are obviously an
enormous number of toxic substances which depress speed, and until
the mechanism of locomotion is better understood this is not a fruitful
field for review. O f the substances which stimulate locomotion, embryo
extract, an exceedingly complicated mixture that strongly accelerates
the locomotion of fibroblasts, is the only one that has been the subject
of critical observation. Willmer (1933) first demonstrated the effect by
actual measurement. Willmer and Jacoby (1936), in a later more
detailed study, found that when chick periosteal fibroblasts in a
plasma-saline medium were given embryo extract, speed began to
increase after 2 h and by 6 h had risen from an initial 7 to about 45/x/h
with the highest concentration (40% of extract) used; lower speeds
were reached with lower concentrations. Curtis (1961) found that with
very high concentrations speeds diminished again.
Next to be considered are the ways that contact with a solid surface
may influence speed. It can hardly be doubted that the nature of the
solid substrate, or of whatever constituents of the liquid medium are
adsorbed to it, will affect speed. The cell must adhere to the substrate
to move, and it is likely that speed will diminish if the adhesion becomes
either too strong or too weak. Data however are lacking.
The effect of the physical conformation of the substrate is in one
respect better documented. Loeb and Fleisher (1917) noted that cells
commonly move faster on the surface of a plasma clot than within it;
but when a plasma clot has its fibrils oriented, cells move almost as fast
in the clot as on it. In an unoriented clot, they suggested, the cells send
out pseudopodia in various directions, while in an oriented clot the cell
is more efficiently polarized; they suggested also that a cell tends to
follow its largest pseudopodium, which is the one attached to the
largest fibril. Closely related was the investigation of Weiss and Garber
(1952), and Garber (1953), in which the movement of fibroblasts was
studied in conditions expected to vary the size of the fibrils in the fibrin
clots used for culture. The coarser the expected size of the fibrin bundles,
the faster the expansion of the cultures. Though measurements were
derived from tracings of the periphery at 24-h intervals, and differences
in the fibrin texture would easily produce different rates of change of
direction, the interpretation of Weiss and Garber seems plausible: that
speed is in fact slower when the cell has numerous small evenly-matched
pseudopodia than when it has one large one which can competitively
suppress the rest.
The other form of contact influence comes from neighbouring cells.
Such an influence is clear in the case of chick heart fibroblasts.
Abercrombie and Heaysman (1953) showed that an increase in the
183
O f the factors influencing speed of movement, we may consider first
diffusible substances in the liquid medium. There are obviously an
enormous number of toxic substances which depress speed, and until
the mechanism of locomotion is better understood this is not a fruitful
field for review. O f the substances which stimulate locomotion, embryo
extract, an exceedingly complicated mixture that strongly accelerates
the locomotion of fibroblasts, is the only one that has been the subject
of critical observation. Willmer (1933) first demonstrated the effect by
actual measurement. Willmer and Jacoby (1936), in a later more
detailed study, found that when chick periosteal fibroblasts in a
plasma-saline medium were given embryo extract, speed began to
increase after 2 h and by 6 h had risen from an initial 7 to about 45/x/h
with the highest concentration (40% of extract) used; lower speeds
were reached with lower concentrations. Curtis (1961) found that with
very high concentrations speeds diminished again.
Next to be considered are the ways that contact with a solid surface
may influence speed. It can hardly be doubted that the nature of the
solid substrate, or of whatever constituents of the liquid medium are
adsorbed to it, will affect speed. The cell must adhere to the substrate
to move, and it is likely that speed will diminish if the adhesion becomes
either too strong or too weak. Data however are lacking.
The effect of the physical conformation of the substrate is in one
respect better documented. Loeb and Fleisher (1917) noted that cells
commonly move faster on the surface of a plasma clot than within it;
but when a plasma clot has its fibrils oriented, cells move almost as fast
in the clot as on it. In an unoriented clot, they suggested, the cells send
out pseudopodia in various directions, while in an oriented clot the cell
is more efficiently polarized; they suggested also that a cell tends to
follow its largest pseudopodium, which is the one attached to the
largest fibril. Closely related was the investigation of Weiss and Garber
(1952), and Garber (1953), in which the movement of fibroblasts was
studied in conditions expected to vary the size of the fibrils in the fibrin
clots used for culture. The coarser the expected size of the fibrin bundles,
the faster the expansion of the cultures. Though measurements were
derived from tracings of the periphery at 24-h intervals, and differences
in the fibrin texture would easily produce different rates of change of
direction, the interpretation of Weiss and Garber seems plausible: that
speed is in fact slower when the cell has numerous small evenly-matched
pseudopodia than when it has one large one which can competitively
suppress the rest.
The other form of contact influence comes from neighbouring cells.
Such an influence is clear in the case of chick heart fibroblasts.
Abercrombie and Heaysman (1953) showed that an increase in the