32
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W l L L M E R
position. This coating of celloidin forms a reliable standardized
surface.
Most cells, when they emerge and creep on the glass (or celloidin)
become relatively flattened in the plane of the glass, if they do not
actually "dedifferentiate" to an even greater extent. In this flattening
there appear to be two rather different processes at work, initial
adherence to the glass and subsequent flattening and migration
(Taylor, 1961). The factors which allow the cells to adhere to the glass
are sometimes different from those which later cause them to flatten
and migrate. The coating of cholesterol mentioned above facilitates
adhesion to the glass surface but does not help the flattening of the cells.
Among the substances which have been observed to assist in the
spreading out of the cells on glass, though not necessarily in hanging
drop cultures, are serine (Lockart and Eagle, 1959), inositol (Eagle,
Oyama, Levy and Freeman, 1957), cephalin (Fujii, 1934, 1941) and
certain factors in serum which are probably proteins or glycoproteins
(Lieberman and Ove, 1958). The spreading in serum may be assisted
by the provision in the serum of nutritional factors, for most cells
survive longer and move more actively when serum is present, though
it alone does not support the multiplication of normal mechanocytes
for very long. A glycoprotein (fetuin) prepared from foetal calf serum
(Puck, 1961) has been found to be very active in causing cells to spread.
Certain basic polypeptides also assist cells to attach to glass (Lieberman
and Ove, 1958). Similar problems are discussed in other contexts (see
pp. 63, 291, 493, 500).
A cell which has flattened itself against a glass surface in a hangingdrop culture, or indeed in any other form of culture, is in a very different
situation from that which it occupied in the body, and it is well to
remember that, in the body, glass and other smooth surfaces can evoke
"foreign-body reactions" from tissues, and have even been suspected
of causing malignant changes. As indicated earlier, other surfaces
besides glass have been tried from time to time as suitable supporting
surfaces for cultures. Quartz (which is of course necessary when u.v.
light is being used), mica and well-washed Cellophane are reasonably
harmless, and other inert substances could no doubt be used, though
some of the synthetic polymers such as polythene or Perspex often
contain sufficient toxic materials to make them unsatisfactory and some
of them are non-wettable. Coverslips which have been coated with
reconstituted collagen (Ehrmann and Gey, 1956) offer a better grip
for some types of cell and probably provide a rather more physiological environment for the cells which adhere to it. The use of celloidin
in this way has already been mentioned.
The ions attached to the surface of glass, or those which may be
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W l L L M E R
position. This coating of celloidin forms a reliable standardized
surface.
Most cells, when they emerge and creep on the glass (or celloidin)
become relatively flattened in the plane of the glass, if they do not
actually "dedifferentiate" to an even greater extent. In this flattening
there appear to be two rather different processes at work, initial
adherence to the glass and subsequent flattening and migration
(Taylor, 1961). The factors which allow the cells to adhere to the glass
are sometimes different from those which later cause them to flatten
and migrate. The coating of cholesterol mentioned above facilitates
adhesion to the glass surface but does not help the flattening of the cells.
Among the substances which have been observed to assist in the
spreading out of the cells on glass, though not necessarily in hanging
drop cultures, are serine (Lockart and Eagle, 1959), inositol (Eagle,
Oyama, Levy and Freeman, 1957), cephalin (Fujii, 1934, 1941) and
certain factors in serum which are probably proteins or glycoproteins
(Lieberman and Ove, 1958). The spreading in serum may be assisted
by the provision in the serum of nutritional factors, for most cells
survive longer and move more actively when serum is present, though
it alone does not support the multiplication of normal mechanocytes
for very long. A glycoprotein (fetuin) prepared from foetal calf serum
(Puck, 1961) has been found to be very active in causing cells to spread.
Certain basic polypeptides also assist cells to attach to glass (Lieberman
and Ove, 1958). Similar problems are discussed in other contexts (see
pp. 63, 291, 493, 500).
A cell which has flattened itself against a glass surface in a hangingdrop culture, or indeed in any other form of culture, is in a very different
situation from that which it occupied in the body, and it is well to
remember that, in the body, glass and other smooth surfaces can evoke
"foreign-body reactions" from tissues, and have even been suspected
of causing malignant changes. As indicated earlier, other surfaces
besides glass have been tried from time to time as suitable supporting
surfaces for cultures. Quartz (which is of course necessary when u.v.
light is being used), mica and well-washed Cellophane are reasonably
harmless, and other inert substances could no doubt be used, though
some of the synthetic polymers such as polythene or Perspex often
contain sufficient toxic materials to make them unsatisfactory and some
of them are non-wettable. Coverslips which have been coated with
reconstituted collagen (Ehrmann and Gey, 1956) offer a better grip
for some types of cell and probably provide a rather more physiological environment for the cells which adhere to it. The use of celloidin
in this way has already been mentioned.
The ions attached to the surface of glass, or those which may be