180
M. A B E R C R O M B I E
properties may often depend on the activities of the cell population
itself in consuming or producing substances. Such diffusible stimulants
obviously readily give rise to co-ordinated behaviour throughout a
population. Contact stimulation depends on the structure of a surface
apposed to the cell, acting perhaps through the mechanical effects of
adhesion (e.g. Curtis, 1960) or by orientation of the molecules making
up the cell surface (Weiss, 1961) or change in the "molecular ecology"
of the cell surface (Weiss, 1947). Contact itself is, of course, really a
matter of degree, but distances of up to a few hundred A are in practice
involved. The stimulating surface may be non-cellular, and this form of
contact is important in tissue culture because of the large areas of
artificial solid substrate provided; or it may belong to another cell.
Co-ordinated behaviour within a cell population is not peculiarly the
result of diffusive stimuli; it may be produced via contact stimuli, both
because the structure of a large area of substrate may be influenced
from a remote source, as in Weiss's two-centre effect described below,
and because contact stimuli may be relayed from cell to cell, as in the
population effects of contact inhibition to be discussed.
2. Response
At the beginning of the study of tissue culture, the concepts of animal
behaviour were obviously in the minds of Harrison and Loeb when they
discussed the control of cell locomotion. It is clear that the theoretical
framework developed for the simpler aspects of animal locomotory
behaviour (see especially Fraenkel and Gunn, 1961; Patlak, 1953a, b)
must continue to be valuable to the student of cell behaviour. The most
important distinction to be derived from this source is that between
unoriented and oriented responses.
In an unoriented response, a cell undergoes some change in its
locomotion in response, not to a patterned cue from its environment,
but to the local intensity of some scalar property, averaged out over the
whole cell. As a result the cell may change the rate of a random component in its movement: it may alter its average speed, without
diminishing the randomness of the variations in its speed; or it may
alter the number of random changes of direction it makes per unit of
time (or per unit of distance travelled). These are the pure kineses of
animal behaviour. Even in an environment that is effectively unstructured, however, a cell is likely to have non-random components in its
movement; that is to say it may not move by "random walk" (Patlak,
1953a) with successive steps independent of each other in speed,
length, and direction. It may have an internal bias, an autonomous
form of movement which is non-random in this sense; and an unorientated response to the local intensity of some property of its sur-
M. A B E R C R O M B I E
properties may often depend on the activities of the cell population
itself in consuming or producing substances. Such diffusible stimulants
obviously readily give rise to co-ordinated behaviour throughout a
population. Contact stimulation depends on the structure of a surface
apposed to the cell, acting perhaps through the mechanical effects of
adhesion (e.g. Curtis, 1960) or by orientation of the molecules making
up the cell surface (Weiss, 1961) or change in the "molecular ecology"
of the cell surface (Weiss, 1947). Contact itself is, of course, really a
matter of degree, but distances of up to a few hundred A are in practice
involved. The stimulating surface may be non-cellular, and this form of
contact is important in tissue culture because of the large areas of
artificial solid substrate provided; or it may belong to another cell.
Co-ordinated behaviour within a cell population is not peculiarly the
result of diffusive stimuli; it may be produced via contact stimuli, both
because the structure of a large area of substrate may be influenced
from a remote source, as in Weiss's two-centre effect described below,
and because contact stimuli may be relayed from cell to cell, as in the
population effects of contact inhibition to be discussed.
2. Response
At the beginning of the study of tissue culture, the concepts of animal
behaviour were obviously in the minds of Harrison and Loeb when they
discussed the control of cell locomotion. It is clear that the theoretical
framework developed for the simpler aspects of animal locomotory
behaviour (see especially Fraenkel and Gunn, 1961; Patlak, 1953a, b)
must continue to be valuable to the student of cell behaviour. The most
important distinction to be derived from this source is that between
unoriented and oriented responses.
In an unoriented response, a cell undergoes some change in its
locomotion in response, not to a patterned cue from its environment,
but to the local intensity of some scalar property, averaged out over the
whole cell. As a result the cell may change the rate of a random component in its movement: it may alter its average speed, without
diminishing the randomness of the variations in its speed; or it may
alter the number of random changes of direction it makes per unit of
time (or per unit of distance travelled). These are the pure kineses of
animal behaviour. Even in an environment that is effectively unstructured, however, a cell is likely to have non-random components in its
movement; that is to say it may not move by "random walk" (Patlak,
1953a) with successive steps independent of each other in speed,
length, and direction. It may have an internal bias, an autonomous
form of movement which is non-random in this sense; and an unorientated response to the local intensity of some property of its sur-