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
179
cell usually appears to glide, sometimes rather jerkily as adhesions to its
surroundings break free. Observations with the surface contact microscope (Ambrose, 1961) have suggested that translocation is produced by
a system of transverse and longitudinal waves in that surface of the cell
which makes contact with the substrate, mainly in the region of the
ruffled membrane.
Somewhat similar leading ruffled membranes are found on many
other kinds of vertebrate tissue-cell: for example on epithelia, at the free
edge of a sheet of cells (Harrison, 1910); on melanoblasts (Algard, 1953);
and on Schwann cells (Lubinska, 1961). Neurites often have a membrane
at the advancing tip, with radiating thickenings (Harrison, 1910;
Hughes, 1953), though sometimes they have actively moving filamentous projections—filopodia—instead (Nakai and Kawasaki, 1959),
which may also appear on other parts of the neurite (Lewis and Lewis,
1912). A ruffled membrane may even appear on the cell body of a
moving neuroblast with neurites already extended (Olivo, 1927). It is
quite probable that all these tissue cells move fundamentally like a
fibroblast.
Vertebrate amoebocytes (white blood cells and macrophages) on the
other hand frequently show a conspicuous forward flow of the cytoplasm (Lewis, 1927); and correspondingly parts of the edge of the cell
may be obviously stationary in relation to the substrate, while cytoplasm flows past (Rioch, 1923; De Bruyn, 1946). A ruffled membrane
is a striking feature of the macrophage, but polymorphs and lymphocytes have much less prominent membranous or filamentous processes
at the anterior border of the pseudopodium (Rioch, 1923; Lewis, 1927;
Rich, Wintrobe and Lewis, 1939). The anterior region of the moving
cell is again the part most closely adherent to the substrate (Lewis,
1931; De Bruyn, 1946). Amoebocytes and "fixed" cells thus appear to
move in a somewhat different way, and they also move at very different
speeds. It is not yet possible to say how these apparently distinct modes
of movement are related.
B. STIMULUS A N D RESPONSE
1. Stimulus
The major problem in the investigation of cell behaviour is to
analyse the variations in speed and direction of movement of cells into
responses to certain components of their external environment. The
relevant components to which most attention has been given provide
stimuli to cells of two kinds: those depending on substances dissolved
and diffusing in the fluid medium, and those depending on contact with
solid surroundings. Concentrations and concentration-gradients are the
properties concerned in the action of the diffusible stimulants, and these
179
cell usually appears to glide, sometimes rather jerkily as adhesions to its
surroundings break free. Observations with the surface contact microscope (Ambrose, 1961) have suggested that translocation is produced by
a system of transverse and longitudinal waves in that surface of the cell
which makes contact with the substrate, mainly in the region of the
ruffled membrane.
Somewhat similar leading ruffled membranes are found on many
other kinds of vertebrate tissue-cell: for example on epithelia, at the free
edge of a sheet of cells (Harrison, 1910); on melanoblasts (Algard, 1953);
and on Schwann cells (Lubinska, 1961). Neurites often have a membrane
at the advancing tip, with radiating thickenings (Harrison, 1910;
Hughes, 1953), though sometimes they have actively moving filamentous projections—filopodia—instead (Nakai and Kawasaki, 1959),
which may also appear on other parts of the neurite (Lewis and Lewis,
1912). A ruffled membrane may even appear on the cell body of a
moving neuroblast with neurites already extended (Olivo, 1927). It is
quite probable that all these tissue cells move fundamentally like a
fibroblast.
Vertebrate amoebocytes (white blood cells and macrophages) on the
other hand frequently show a conspicuous forward flow of the cytoplasm (Lewis, 1927); and correspondingly parts of the edge of the cell
may be obviously stationary in relation to the substrate, while cytoplasm flows past (Rioch, 1923; De Bruyn, 1946). A ruffled membrane
is a striking feature of the macrophage, but polymorphs and lymphocytes have much less prominent membranous or filamentous processes
at the anterior border of the pseudopodium (Rioch, 1923; Lewis, 1927;
Rich, Wintrobe and Lewis, 1939). The anterior region of the moving
cell is again the part most closely adherent to the substrate (Lewis,
1931; De Bruyn, 1946). Amoebocytes and "fixed" cells thus appear to
move in a somewhat different way, and they also move at very different
speeds. It is not yet possible to say how these apparently distinct modes
of movement are related.
B. STIMULUS A N D RESPONSE
1. Stimulus
The major problem in the investigation of cell behaviour is to
analyse the variations in speed and direction of movement of cells into
responses to certain components of their external environment. The
relevant components to which most attention has been given provide
stimuli to cells of two kinds: those depending on substances dissolved
and diffusing in the fluid medium, and those depending on contact with
solid surroundings. Concentrations and concentration-gradients are the
properties concerned in the action of the diffusible stimulants, and these