130
C H A R I T Y W A Y M O U T H
has identified the role of thyroxine in initiating chick skin differentiation,
has noted the relationship of this inductor system to developmental
age, and has analysed epidermal and dermal interactions in vitro.
I V . F U T U R E PROSPECTS
We may be confident that the major nutrients required by all cells
are now known, and that the amounts in which they may be combined
for successful cultivation of some cells have been roughly established.
Much remains to be done to create conditions under which we can
control, at will, the behaviour of cells in vitro. We can expect to see
media developed for maintaining cells in the diploid state, with or
without proliferation; media to promote specific synthetic capacities
of cells, e.g. hormone production; media to promote functional cellular
differentiation, morphological and chemical; and media for organized
growth and development and intercellular interactions.
After the long, hard path, it is a little discouraging to read the relatively recent opinion that "for one or two of the more hardy races
of cells a limited success has been achieved" with synthetic media
(Willmer, 1960). This statement gives less recognition than would
generally be allowed to the record of successful, prolonged, growth of
cell lines from several species in a wide variety of media. There is,
however, enough truth in his (Willmer, 1960) remark that "pure"
cultures of cells "are remarkable rather for their similarity than for
their differences" in nutritional requirements and metabolic pathways,
a view also expressed by Levintow and Eagle (1961), to make it important to point out that the most extensively studied cell lines have been
isolated under nutritional and environmental conditions which would
tend to be highly selective and would therefore favour this conclusion.
Cells which might be found (under different experimental conditions)
to have different metabolic or nutritional needs would be apt to be
eliminated at the start of the race, and the biochemical characteristics
that we see may reflect at least as much the culture conditions as
properties of the tissue of origin. Progress has been made in establishing,
not absolute requirements, but working ranges of concentrations, of the
various important ingredients of useful media, empirically effective
in the particular test systems used. It is already becoming clear that
qualitative and quantitative differences between cell types—even
between nutritional variants cloned from a single cell type—are
being discerned, and that particularly in organ culture, media promoting special functions can already be made. This makes it hopeful
and probable that principles will emerge to enable us to design nutrients
C H A R I T Y W A Y M O U T H
has identified the role of thyroxine in initiating chick skin differentiation,
has noted the relationship of this inductor system to developmental
age, and has analysed epidermal and dermal interactions in vitro.
I V . F U T U R E PROSPECTS
We may be confident that the major nutrients required by all cells
are now known, and that the amounts in which they may be combined
for successful cultivation of some cells have been roughly established.
Much remains to be done to create conditions under which we can
control, at will, the behaviour of cells in vitro. We can expect to see
media developed for maintaining cells in the diploid state, with or
without proliferation; media to promote specific synthetic capacities
of cells, e.g. hormone production; media to promote functional cellular
differentiation, morphological and chemical; and media for organized
growth and development and intercellular interactions.
After the long, hard path, it is a little discouraging to read the relatively recent opinion that "for one or two of the more hardy races
of cells a limited success has been achieved" with synthetic media
(Willmer, 1960). This statement gives less recognition than would
generally be allowed to the record of successful, prolonged, growth of
cell lines from several species in a wide variety of media. There is,
however, enough truth in his (Willmer, 1960) remark that "pure"
cultures of cells "are remarkable rather for their similarity than for
their differences" in nutritional requirements and metabolic pathways,
a view also expressed by Levintow and Eagle (1961), to make it important to point out that the most extensively studied cell lines have been
isolated under nutritional and environmental conditions which would
tend to be highly selective and would therefore favour this conclusion.
Cells which might be found (under different experimental conditions)
to have different metabolic or nutritional needs would be apt to be
eliminated at the start of the race, and the biochemical characteristics
that we see may reflect at least as much the culture conditions as
properties of the tissue of origin. Progress has been made in establishing,
not absolute requirements, but working ranges of concentrations, of the
various important ingredients of useful media, empirically effective
in the particular test systems used. It is already becoming clear that
qualitative and quantitative differences between cell types—even
between nutritional variants cloned from a single cell type—are
being discerned, and that particularly in organ culture, media promoting special functions can already be made. This makes it hopeful
and probable that principles will emerge to enable us to design nutrients