150
E . N . W I L L M E R
by the fact that, as the cells move away from the original explant and
become more and more isolated from the neighbours which they had
in the original tissues, there is a tendency for them to change their
morphology and to approximate each other in appearance and behaviour, presumably in response to their new surroundings. Some classes
of cells are much more flexible in this way than others. For example,
cells in strains of HeLa cells, which were originally derived from a
carcinoma of the cervix uteri, and which are therefore presumably
some variant on the epitheliocyte, have been shown to adopt forms
characteristic not only of epitheliocytes cohering in flat sheets, or of
epitheliocytes in columnar array, but they may become multinucleate
giant cells, "fibroblastoid" cells, and cells resembling neurones and
astrocytes (Rose, 1962) and these forms cannot be easily related to
recognizable environmental changes (Fig. 2).
It is therefore obvious that static morphological criteria for distinguishing cells in vitro are by themselves of relatively little value, except
in a limited manner in the early stages of life in culture or under those
conditions of culture (organ culture) in which growth is restricted, and
in which the cells are allowed and encouraged to develop in surroundings more nearly like those that they had in the body. Dynamic
morphological criteria are much more valuable, but even these have
their limitations.
A. E X T R I N S I C F A C T O R S
Some of the extrinsic factors which can modify cell form and behaviour may now be profitably considered. As discussed in the chapter
on methods, if the movement of the cell is to occur on a glass coverslip,
for example, it is necessary for the cell to be able not only to make
contact with the glass but also to stick to it and generally to spread
out upon it, and the factors which cause the initial sticking may not
be the same as those which allow the subsequent spreading. Even the
properties of the glass are important and there are great differences
between hard and soft glass (Rappaport, Poole and Rappaport, 1960).
The ionic distribution in the immediate neighbourhood of the cells is
important in determining the behaviour of the surface of the cell. If the
contact with the glass or sub-stratum is inadequate, most cells remain immobile and often round up. When the cells are spread out on the glass
surface, it need hardly be repeated that they are in a grossly abnormal
situation and subject to a wide variety of unusual stimuli. It is not surprising, therefore, that under these conditions they begin to display new
and sometimes peculiar forms of behaviour.
If cotton or other fibres are present in the vicinity of the cells of a
E . N . W I L L M E R
by the fact that, as the cells move away from the original explant and
become more and more isolated from the neighbours which they had
in the original tissues, there is a tendency for them to change their
morphology and to approximate each other in appearance and behaviour, presumably in response to their new surroundings. Some classes
of cells are much more flexible in this way than others. For example,
cells in strains of HeLa cells, which were originally derived from a
carcinoma of the cervix uteri, and which are therefore presumably
some variant on the epitheliocyte, have been shown to adopt forms
characteristic not only of epitheliocytes cohering in flat sheets, or of
epitheliocytes in columnar array, but they may become multinucleate
giant cells, "fibroblastoid" cells, and cells resembling neurones and
astrocytes (Rose, 1962) and these forms cannot be easily related to
recognizable environmental changes (Fig. 2).
It is therefore obvious that static morphological criteria for distinguishing cells in vitro are by themselves of relatively little value, except
in a limited manner in the early stages of life in culture or under those
conditions of culture (organ culture) in which growth is restricted, and
in which the cells are allowed and encouraged to develop in surroundings more nearly like those that they had in the body. Dynamic
morphological criteria are much more valuable, but even these have
their limitations.
A. E X T R I N S I C F A C T O R S
Some of the extrinsic factors which can modify cell form and behaviour may now be profitably considered. As discussed in the chapter
on methods, if the movement of the cell is to occur on a glass coverslip,
for example, it is necessary for the cell to be able not only to make
contact with the glass but also to stick to it and generally to spread
out upon it, and the factors which cause the initial sticking may not
be the same as those which allow the subsequent spreading. Even the
properties of the glass are important and there are great differences
between hard and soft glass (Rappaport, Poole and Rappaport, 1960).
The ionic distribution in the immediate neighbourhood of the cells is
important in determining the behaviour of the surface of the cell. If the
contact with the glass or sub-stratum is inadequate, most cells remain immobile and often round up. When the cells are spread out on the glass
surface, it need hardly be repeated that they are in a grossly abnormal
situation and subject to a wide variety of unusual stimuli. It is not surprising, therefore, that under these conditions they begin to display new
and sometimes peculiar forms of behaviour.
If cotton or other fibres are present in the vicinity of the cells of a