4 . C E L L T Y P E S
167
similarly produced in fibroblasts or macrophages. Since fibroblasts
and macrophages normally live together in a well-regulated environment (as compared with that of Naegleria) it is probable that in them the
two types of activity are more intrinsically fixed and less directly
dependent upon the environment. By opposing each other in their actions they could help to stabilize their whole environment but, just
as there are means of triggering the metamorphosis of Naegleria, so there
may be ways of changing fibroblasts to macrophage and vice versa. T w o
observations are pertinent. First, quaternary ammonium ions favour
the amoeboid form of Naegleria. In tissue cultures of muscle they favour
the growth of macrophages rather than of fibroblasts (Thomas, 1937;
Chevremont and Chevremont-Comhaire, 1945). Secondly, certain
steroids, in particular deoxycorticosterone and progesterone, which in
mammals are known to affect the manner in which certain tissue cells,
e.g. kidney, deal with water and salts or to alter the Na : K ratio in
certain tissues, e.g. myometrium and endometrium (Horvath, 1954),
also determine the phase adopted by Naegleria (Pearson and Willmer,
1963). Thus it might be profitable to seek the transforming agent for
the macrophage—fibroblast transformation among the various agents
which are known to affect the ionic distribution between cells and their
surrounding medium. It might also be revealing to study the relationships between fibroblasts and macrophages in tissue cultures treated
with the appropriate steroids, and to record the growth rates and
migration rates under these conditions.
I X . C E L L S IN C L O N E S A N D P U R E L I N E S
It was mentioned earlier that the mechanocyte was a cell which,
because of its origin, was normally dependent upon the surrounding
epithelial cells, that it was only capable of growing in vitro under rather
special conditions, such as those provided by a medium containing
embryo extract, and that, in cultures, it normally would not live in
isolation but when planted in numbers would make colonies of loosely
connected cells. Countless attempts by early tissue-culturists to make
pure cultures, or clones, of fibroblasts from single cells all failed until,
as discussed in Chapter 2, Sanford, Earle and Likely (1948) enclosed
a few cells from a fibroblast culture in capillary tubes where they had
much more restricted micro-environments than was possible elsewhere
and, in these conditions, isolated cells occasionally divided and went
on to form colonies, though the nature of the cells in these colonies
is still somewhat dubious. It is not yet clear why the fibroblast or
mechanocyte is so much more sensitive in this direction than other
167
similarly produced in fibroblasts or macrophages. Since fibroblasts
and macrophages normally live together in a well-regulated environment (as compared with that of Naegleria) it is probable that in them the
two types of activity are more intrinsically fixed and less directly
dependent upon the environment. By opposing each other in their actions they could help to stabilize their whole environment but, just
as there are means of triggering the metamorphosis of Naegleria, so there
may be ways of changing fibroblasts to macrophage and vice versa. T w o
observations are pertinent. First, quaternary ammonium ions favour
the amoeboid form of Naegleria. In tissue cultures of muscle they favour
the growth of macrophages rather than of fibroblasts (Thomas, 1937;
Chevremont and Chevremont-Comhaire, 1945). Secondly, certain
steroids, in particular deoxycorticosterone and progesterone, which in
mammals are known to affect the manner in which certain tissue cells,
e.g. kidney, deal with water and salts or to alter the Na : K ratio in
certain tissues, e.g. myometrium and endometrium (Horvath, 1954),
also determine the phase adopted by Naegleria (Pearson and Willmer,
1963). Thus it might be profitable to seek the transforming agent for
the macrophage—fibroblast transformation among the various agents
which are known to affect the ionic distribution between cells and their
surrounding medium. It might also be revealing to study the relationships between fibroblasts and macrophages in tissue cultures treated
with the appropriate steroids, and to record the growth rates and
migration rates under these conditions.
I X . C E L L S IN C L O N E S A N D P U R E L I N E S
It was mentioned earlier that the mechanocyte was a cell which,
because of its origin, was normally dependent upon the surrounding
epithelial cells, that it was only capable of growing in vitro under rather
special conditions, such as those provided by a medium containing
embryo extract, and that, in cultures, it normally would not live in
isolation but when planted in numbers would make colonies of loosely
connected cells. Countless attempts by early tissue-culturists to make
pure cultures, or clones, of fibroblasts from single cells all failed until,
as discussed in Chapter 2, Sanford, Earle and Likely (1948) enclosed
a few cells from a fibroblast culture in capillary tubes where they had
much more restricted micro-environments than was possible elsewhere
and, in these conditions, isolated cells occasionally divided and went
on to form colonies, though the nature of the cells in these colonies
is still somewhat dubious. It is not yet clear why the fibroblast or
mechanocyte is so much more sensitive in this direction than other