124
C H A R I T Y W A Y M O U T H
divergent activities with respect to certain enzymes (Scott, Pakoskey and
Sanford, 1960). Experience in this laboratory, where sublines of clone
N C T C 929 have been kept in a number of different synthetic media
for periods of several years, demonstrates that distinct morphological
characteristics develop in the sublines, easily recognizable on lowpower microscopic inspection. T w o sublines in the same medium, but
with different previous nutritional histories, may also have distinctive
cellular morphologies and dissimilar colonial patterns. Reports from
many laboratories show that clones and sublines may manifest differences in karyotype, in enzyme activities, in tumour-producing activities,
and in other clearly demonstrable characters.
So, while admitting that changes in the cells are an important
factor in "adaptation", it must be emphasized that improvements in
the composition of the medium, making an environment more suitable
for the cells, can go a long way, and may eventually go all the way,
towards eliminating the difficulties we now experience in getting cells
through the transition stages from biological to synthetic media, and
from in vivo to in vitro life. Adaptation of media to suit particular cells
must be considered at least as important as adaptation of cells to
arbitrarily chosen, empirically designed, media, which may be only
very approximate substitutes for the natural environment of the cells.
The question of adaptation of the environment to suit the cells is
closely related to that of the minimum inoculum size for successful
growth in culture. Very early, the fact that single cells, or very small
explants, fail to survive, where a large population of the same cells
in the same medium will grow, was remarked upon (Burrows, 1926;
Earle and Thompson, 1930). W e remain aware of what Willmer (1960)
calls the "extraordinary importance of the immediate and intimate
environments of each cell in a tissue". A great part of the microenvironment of each cell is usually other cells, and Tissue Culture
experience bears out the social character of a cell population. Singlecell cloning failed for a long time after cultivation of large numbers
of cells had become a routine technique, and it had to be supposed
that cells provide some kind of mutual support to each other. An
artificial micro-environment capable of permitting survival and growth
of single cells must be much more carefully balanced than the environment which will serve for a large cell population. The minimum
inoculum necessary for establishing growth under different conditions
has been studied (Earle, Bryant and Schilling, 1954; Pace and Aftonomos, 1957; Fioramonti, Evans and Earle, 1958). Diffusion of limiting
nutrients away from the cells has been proposed as the main reason
for failure of isolated cells to survive. Conversely, provision of conditions
which restrict diffusion (confinement of cells within a capillary,
C H A R I T Y W A Y M O U T H
divergent activities with respect to certain enzymes (Scott, Pakoskey and
Sanford, 1960). Experience in this laboratory, where sublines of clone
N C T C 929 have been kept in a number of different synthetic media
for periods of several years, demonstrates that distinct morphological
characteristics develop in the sublines, easily recognizable on lowpower microscopic inspection. T w o sublines in the same medium, but
with different previous nutritional histories, may also have distinctive
cellular morphologies and dissimilar colonial patterns. Reports from
many laboratories show that clones and sublines may manifest differences in karyotype, in enzyme activities, in tumour-producing activities,
and in other clearly demonstrable characters.
So, while admitting that changes in the cells are an important
factor in "adaptation", it must be emphasized that improvements in
the composition of the medium, making an environment more suitable
for the cells, can go a long way, and may eventually go all the way,
towards eliminating the difficulties we now experience in getting cells
through the transition stages from biological to synthetic media, and
from in vivo to in vitro life. Adaptation of media to suit particular cells
must be considered at least as important as adaptation of cells to
arbitrarily chosen, empirically designed, media, which may be only
very approximate substitutes for the natural environment of the cells.
The question of adaptation of the environment to suit the cells is
closely related to that of the minimum inoculum size for successful
growth in culture. Very early, the fact that single cells, or very small
explants, fail to survive, where a large population of the same cells
in the same medium will grow, was remarked upon (Burrows, 1926;
Earle and Thompson, 1930). W e remain aware of what Willmer (1960)
calls the "extraordinary importance of the immediate and intimate
environments of each cell in a tissue". A great part of the microenvironment of each cell is usually other cells, and Tissue Culture
experience bears out the social character of a cell population. Singlecell cloning failed for a long time after cultivation of large numbers
of cells had become a routine technique, and it had to be supposed
that cells provide some kind of mutual support to each other. An
artificial micro-environment capable of permitting survival and growth
of single cells must be much more carefully balanced than the environment which will serve for a large cell population. The minimum
inoculum necessary for establishing growth under different conditions
has been studied (Earle, Bryant and Schilling, 1954; Pace and Aftonomos, 1957; Fioramonti, Evans and Earle, 1958). Diffusion of limiting
nutrients away from the cells has been proposed as the main reason
for failure of isolated cells to survive. Conversely, provision of conditions
which restrict diffusion (confinement of cells within a capillary,