THE ACRASINA
157
or even an understanding of the mechanism of chemotaxis: because
communication is extracellular, it is an admirable system for studying
the controls by which an initially chaotic population acquires a definite
structure, which for good measure, is not merely chemical but morphological too. And even if many of the speculations that have been offered
(Section IV, B, 1) prove to be far wide of the mark, they may yet have
served some purpose in drawing attention to the sort of sophisticated
biochemical dynamics that must be involved. By what psychic insight
did Bonner name acrasin after a witch (see Shaffer, 1957a)? It is indeed,
as Revelation has it, a synagogue of Satan.
D. The Nature of Intercellular Bonding
The strength of intercellular adhesion is seen in surgical operations on
streams (Bonner, 1950; Shaffer, 1957b), and, when very young P.
violaceum centres are dispersed, in the way cells cling much more tenaciously to the founders than to any other cells (Shaffer, 1961a). With
most strains of violaceum, in ordinary agar plates, the contrast between
the strongly adhesive, secreting cells in an aggregation and the quite
separate, nonsecreting ones just beyond it, or released from one, is very
considerable. And to emphasize the importance of the change to the
aggregated state, induced by acrasin, it has been called 'integration',
as the opposite of disintegration (Shaffer, 1958), though the name is not
entirely happy, as an aggregation is much less a unit than is a grex. The
same terms can be applied to other species, though the distinction may
become rather blurred, because cells may exist for a considerable time
in a slightly adhesive state (Section IV, B). Despite these changes in
adhesion being rapid, spontaneously reversible and often synchronized,
they are not apparently fundamentally different from alterations in part
or the whole of the metazoan cell surface in vitro. This resemblance is
emphasized by electron micrographs, which show that each amoeba has
a three-layered surface membrane (i.e., two impregnated by osmium
with a less opaque one in between) and that aggregated cells gradually
pack closer together till adjacent membranes are separated by a lighter
layer of fairly constant thickness (^200 Ä), much as in unspecialized
metazoan epithelia (Gezelius, 1959; Mercer and Shaffer, 1960, and in
Bonner, 1959a). Whether or not the material in this intermediate layer
is regarded as part of the surface, it is easily displaced, for granules
trapped between cells make contact with the dense membranes (Mercer
and Shaffer, unpublished). If it is important in adhesion, it must be
rendered ineffective during disintegration.
Of the few enzymes tested, hyaluronidase has no effect on aggregates
(Bonner, privately); trypsin at high pH disperses them (Sussman,
1958); and ribonuclease (Shaffer, 1961b; cf. Curtis, 1958; Brächet, 1960)
F2
A . C . 2
157
or even an understanding of the mechanism of chemotaxis: because
communication is extracellular, it is an admirable system for studying
the controls by which an initially chaotic population acquires a definite
structure, which for good measure, is not merely chemical but morphological too. And even if many of the speculations that have been offered
(Section IV, B, 1) prove to be far wide of the mark, they may yet have
served some purpose in drawing attention to the sort of sophisticated
biochemical dynamics that must be involved. By what psychic insight
did Bonner name acrasin after a witch (see Shaffer, 1957a)? It is indeed,
as Revelation has it, a synagogue of Satan.
D. The Nature of Intercellular Bonding
The strength of intercellular adhesion is seen in surgical operations on
streams (Bonner, 1950; Shaffer, 1957b), and, when very young P.
violaceum centres are dispersed, in the way cells cling much more tenaciously to the founders than to any other cells (Shaffer, 1961a). With
most strains of violaceum, in ordinary agar plates, the contrast between
the strongly adhesive, secreting cells in an aggregation and the quite
separate, nonsecreting ones just beyond it, or released from one, is very
considerable. And to emphasize the importance of the change to the
aggregated state, induced by acrasin, it has been called 'integration',
as the opposite of disintegration (Shaffer, 1958), though the name is not
entirely happy, as an aggregation is much less a unit than is a grex. The
same terms can be applied to other species, though the distinction may
become rather blurred, because cells may exist for a considerable time
in a slightly adhesive state (Section IV, B). Despite these changes in
adhesion being rapid, spontaneously reversible and often synchronized,
they are not apparently fundamentally different from alterations in part
or the whole of the metazoan cell surface in vitro. This resemblance is
emphasized by electron micrographs, which show that each amoeba has
a three-layered surface membrane (i.e., two impregnated by osmium
with a less opaque one in between) and that aggregated cells gradually
pack closer together till adjacent membranes are separated by a lighter
layer of fairly constant thickness (^200 Ä), much as in unspecialized
metazoan epithelia (Gezelius, 1959; Mercer and Shaffer, 1960, and in
Bonner, 1959a). Whether or not the material in this intermediate layer
is regarded as part of the surface, it is easily displaced, for granules
trapped between cells make contact with the dense membranes (Mercer
and Shaffer, unpublished). If it is important in adhesion, it must be
rendered ineffective during disintegration.
Of the few enzymes tested, hyaluronidase has no effect on aggregates
(Bonner, privately); trypsin at high pH disperses them (Sussman,
1958); and ribonuclease (Shaffer, 1961b; cf. Curtis, 1958; Brächet, 1960)
F2
A . C . 2