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
185
sion certainly seems more likely than that there is a controlling centre
in the cell; but their further supposition that the competition is between
streams of cytoplasm, the larger stream draining away material that
might be available for a smaller one, needs to be reconciled with the
apparent absence of streaming during much fibroblast movement. It is
also difficult to apply to the movement of neurites (Hughes, 1953).
Curtis (1960) has suggested that the surface around a ruffled membrane
is contracted, with consequent lower adhesion and increased viscosity,
thus inhibiting the development of new membranes.
Environmentally induced variations in the total amount that a cell
turns in a given time, the "rate of change of direction" of Ullyott
(Fraenkel and Gunn, 1961) is of some importance in animal behaviour
(klinokinesis) but it remains to be studied in cells. Inadvertently, as
already mentioned, rate of change of direction biases estimates of speed,
the more seriously so the longer the time intervals between records of
position.
D. O R I E N T E D RESPONSES
The unoriented responses so far considered can produce effects on the
distribution of cells which may sometimes be of morphogenetic interest,
and they may also affect the rapidity with which oriented responses are
carried out and hence the timing of other morphogenetic events. It is,
however, those movements of cells which are directed in relation to
their environment which most obviously call for explanation in the
study of morphogenesis.
1. Oriented Responses Due to Concentration Gradients of Diffusible Substances
Some of the general problems of chemotaxis in cells are considered
by Shaffer (1957). In the history of the subject of cell behaviour, the
idea that cells move up a concentration gradient towards the source of
a diffusible substance has shown itself to be highly attractive to any
student of morphogenetic movement in search of a hypothesis. In the
circumstances it is disappointing that it has never been satisfactorily
demonstrated to occur in any of the animal cells that the student is
interested in, but only in polymorphs and monocytes. All experiments
purporting to show it that have been made with the cells in a plasma
clot, as so many have been, are suspect: Weiss (1934) pointed out the
probability that oriented structure will be induced in the clot, bringing
into play the powerful influence of contact guidance. Nevertheless the
chemotactic response can be made by some cells. Vertebrate polymorphs and monocytes manifest it towards certain bacterial products,
without apparently any specificity in the relation between attracting
substance and cell type. According to Dixon and McCutcheon (1936)
185
sion certainly seems more likely than that there is a controlling centre
in the cell; but their further supposition that the competition is between
streams of cytoplasm, the larger stream draining away material that
might be available for a smaller one, needs to be reconciled with the
apparent absence of streaming during much fibroblast movement. It is
also difficult to apply to the movement of neurites (Hughes, 1953).
Curtis (1960) has suggested that the surface around a ruffled membrane
is contracted, with consequent lower adhesion and increased viscosity,
thus inhibiting the development of new membranes.
Environmentally induced variations in the total amount that a cell
turns in a given time, the "rate of change of direction" of Ullyott
(Fraenkel and Gunn, 1961) is of some importance in animal behaviour
(klinokinesis) but it remains to be studied in cells. Inadvertently, as
already mentioned, rate of change of direction biases estimates of speed,
the more seriously so the longer the time intervals between records of
position.
D. O R I E N T E D RESPONSES
The unoriented responses so far considered can produce effects on the
distribution of cells which may sometimes be of morphogenetic interest,
and they may also affect the rapidity with which oriented responses are
carried out and hence the timing of other morphogenetic events. It is,
however, those movements of cells which are directed in relation to
their environment which most obviously call for explanation in the
study of morphogenesis.
1. Oriented Responses Due to Concentration Gradients of Diffusible Substances
Some of the general problems of chemotaxis in cells are considered
by Shaffer (1957). In the history of the subject of cell behaviour, the
idea that cells move up a concentration gradient towards the source of
a diffusible substance has shown itself to be highly attractive to any
student of morphogenetic movement in search of a hypothesis. In the
circumstances it is disappointing that it has never been satisfactorily
demonstrated to occur in any of the animal cells that the student is
interested in, but only in polymorphs and monocytes. All experiments
purporting to show it that have been made with the cells in a plasma
clot, as so many have been, are suspect: Weiss (1934) pointed out the
probability that oriented structure will be induced in the clot, bringing
into play the powerful influence of contact guidance. Nevertheless the
chemotactic response can be made by some cells. Vertebrate polymorphs and monocytes manifest it towards certain bacterial products,
without apparently any specificity in the relation between attracting
substance and cell type. According to Dixon and McCutcheon (1936)