36
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W I L L M E R
One of the most important functions of plasma in the culture medium
may be that it slows down the interchange between the contents of the
cells and those of the medium, and thus allows the cells to build up
local environments around themselves which are more favourable to
further cellular activity than the bulk of the medium would be. Plasma
cultures can be washed with embryo juice, heparinized plasma, serum
or saline media and survive well, while similar cells growing in fluid
hanging-drops are easily and sometimes irrevocably damaged by such
treatment.
Although plasma is thus an excellent medium for supporting the
growth and activity of cells in vitro, and one which is easy to obtain,
these advantages are considerably offset by the fact that its chemical
composition is both variable and incompletely defined. The plasma
varies with the animal from which it is obtained and with the physiological state of that animal. Although these variations can be reduced
by pooling the plasma from several animals and storing it frozen-dried,
the chemical composition of such a standard "batch" is still not
completely known and different "batches" may vary. Particular difficulty arises when the effects of hormones or vitamins are being studied,
for allowance has to be made for the presence of these, and perhaps
also their antagonists, in the plasma itself. For these reasons, great
efforts have been made to develop completely synthetic media which
could replace those of biological origin, and the considerable success
in this direction (Chapter 3) has led to a progressive decline in the use
of both plasma and embryo extract.
3. Advantages and Disadvantages of the Hanging-drop Method
The hanging-drop method is extremely convenient for many
purposes, and is particularly useful for maintaining strains of cells
in small quantities though in this it is now being superseded by coldstorage methods (see p. 28). It is relatively easy, requiring little special
equipment; contamination by micro-organisms rarely occurs if ordinary
precautions are taken; should it do so, it is usually confined to a few
cultures and therefore not disastrous. The outgrowing cells are excellently displayed for immediate microscopic study, both alive and
after fixation. For phase-contrast and other critical observations on the
cells in life, it may be necessary to remove the coverslip from the
hollow-ground slide and mount it on a plane surface, in order to
improve the optical qualities of the system. Though this may be
deleterious to the cells in the end, observations can sometimes be made
for some hours. For such purposes, however, the use of slide chambers
(see pp. 38-9) is generally preferable.
The explant of a hanging-drop culture can readily be fixed, sectioned
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W I L L M E R
One of the most important functions of plasma in the culture medium
may be that it slows down the interchange between the contents of the
cells and those of the medium, and thus allows the cells to build up
local environments around themselves which are more favourable to
further cellular activity than the bulk of the medium would be. Plasma
cultures can be washed with embryo juice, heparinized plasma, serum
or saline media and survive well, while similar cells growing in fluid
hanging-drops are easily and sometimes irrevocably damaged by such
treatment.
Although plasma is thus an excellent medium for supporting the
growth and activity of cells in vitro, and one which is easy to obtain,
these advantages are considerably offset by the fact that its chemical
composition is both variable and incompletely defined. The plasma
varies with the animal from which it is obtained and with the physiological state of that animal. Although these variations can be reduced
by pooling the plasma from several animals and storing it frozen-dried,
the chemical composition of such a standard "batch" is still not
completely known and different "batches" may vary. Particular difficulty arises when the effects of hormones or vitamins are being studied,
for allowance has to be made for the presence of these, and perhaps
also their antagonists, in the plasma itself. For these reasons, great
efforts have been made to develop completely synthetic media which
could replace those of biological origin, and the considerable success
in this direction (Chapter 3) has led to a progressive decline in the use
of both plasma and embryo extract.
3. Advantages and Disadvantages of the Hanging-drop Method
The hanging-drop method is extremely convenient for many
purposes, and is particularly useful for maintaining strains of cells
in small quantities though in this it is now being superseded by coldstorage methods (see p. 28). It is relatively easy, requiring little special
equipment; contamination by micro-organisms rarely occurs if ordinary
precautions are taken; should it do so, it is usually confined to a few
cultures and therefore not disastrous. The outgrowing cells are excellently displayed for immediate microscopic study, both alive and
after fixation. For phase-contrast and other critical observations on the
cells in life, it may be necessary to remove the coverslip from the
hollow-ground slide and mount it on a plane surface, in order to
improve the optical qualities of the system. Though this may be
deleterious to the cells in the end, observations can sometimes be made
for some hours. For such purposes, however, the use of slide chambers
(see pp. 38-9) is generally preferable.
The explant of a hanging-drop culture can readily be fixed, sectioned