34
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
imate chromosome counts. The far-reaching results which have since
been obtained by the use of this technique and its subsequent modifications form the subject matter for Chapter 12, from which it will be
appreciated that this simple method of Tissue Culture has much to
offer in this field of genetical study.
Brief reference has already been made to extracts of embryonic
tissues. Since such extracts have been and still are widely used to
stimulate growth in cultures, it may be of interest to give some brief
account of their properties, though the improvement in synthetic media
promises to lessen their importance. When embryo tissues are minced
or pulped, they liberate a considerable quantity of fluid or juice which
can be separated from the tissue fragments by thorough centrifugation
as a colourless and slightly opalescent fluid. It should be stressed that for
most purposes the centrifugation must be sufficiently thorough to
eliminate all viable cells with certainty; otherwise these may readily
contaminate the cell strains to which the extract is later applied (see
p. 170). If the embryos, after being washed in a suitable saline medium
(e.g. Tyrode's solution) are crushed or minced and then centrifuged,
the undiluted supernatant fluid is regarded as 100% embryo juice;
10-day chick embryos form a convenient source, but embryos of other
species or age can be used almost equally well. For practical purposes
the neat juice may be diluted down to something between 10 and 20°/o
with a suitable physiological salt solution, and it will still encourage the
outwandering and division of those cells (mostly mechanocytes) which
it activates. It remains relatively active after being frozen-dried. It
should be noted that embryo juice or extract does not in fact benefit all
classes of cells equally and some cells derive no benefit at all from it.
Of those that do benefit, each has its own optimal concentration
(Parker, 1929, 1933; Willmer and Jacoby, 1936).
In spite of the numerous investigations which have been made on the
subject, the cause of the beneficial action of the extract on both cell
migration and mitosis is still uncertain. No fractionation of the extract
has so far yielded any one specific active principle. The extract probably contains a variety of factors each contributing something to the
welfare of the cells. Its dialysable constituents may be important in
temporarily stimulating both mitosis and cell migration (Jacoby, 1937),
but other factors are also present in the non-dialysable portion which
also contribute to its beneficial action, particularly in relation to longterm cultures. Among other things, it probably helps to compensate for
the dilution of diffusible cell constituents which must always tend to
occur when cells are suspended in relatively large volumes of a fluid
whose composition is not identical with that of the cytoplasm. Ribosenucleoproteins would fall into this category and there is some evidence
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
imate chromosome counts. The far-reaching results which have since
been obtained by the use of this technique and its subsequent modifications form the subject matter for Chapter 12, from which it will be
appreciated that this simple method of Tissue Culture has much to
offer in this field of genetical study.
Brief reference has already been made to extracts of embryonic
tissues. Since such extracts have been and still are widely used to
stimulate growth in cultures, it may be of interest to give some brief
account of their properties, though the improvement in synthetic media
promises to lessen their importance. When embryo tissues are minced
or pulped, they liberate a considerable quantity of fluid or juice which
can be separated from the tissue fragments by thorough centrifugation
as a colourless and slightly opalescent fluid. It should be stressed that for
most purposes the centrifugation must be sufficiently thorough to
eliminate all viable cells with certainty; otherwise these may readily
contaminate the cell strains to which the extract is later applied (see
p. 170). If the embryos, after being washed in a suitable saline medium
(e.g. Tyrode's solution) are crushed or minced and then centrifuged,
the undiluted supernatant fluid is regarded as 100% embryo juice;
10-day chick embryos form a convenient source, but embryos of other
species or age can be used almost equally well. For practical purposes
the neat juice may be diluted down to something between 10 and 20°/o
with a suitable physiological salt solution, and it will still encourage the
outwandering and division of those cells (mostly mechanocytes) which
it activates. It remains relatively active after being frozen-dried. It
should be noted that embryo juice or extract does not in fact benefit all
classes of cells equally and some cells derive no benefit at all from it.
Of those that do benefit, each has its own optimal concentration
(Parker, 1929, 1933; Willmer and Jacoby, 1936).
In spite of the numerous investigations which have been made on the
subject, the cause of the beneficial action of the extract on both cell
migration and mitosis is still uncertain. No fractionation of the extract
has so far yielded any one specific active principle. The extract probably contains a variety of factors each contributing something to the
welfare of the cells. Its dialysable constituents may be important in
temporarily stimulating both mitosis and cell migration (Jacoby, 1937),
but other factors are also present in the non-dialysable portion which
also contribute to its beneficial action, particularly in relation to longterm cultures. Among other things, it probably helps to compensate for
the dilution of diffusible cell constituents which must always tend to
occur when cells are suspended in relatively large volumes of a fluid
whose composition is not identical with that of the cytoplasm. Ribosenucleoproteins would fall into this category and there is some evidence