264
RUTH BELLAIRS
technique. Britt and Herrmann (1959) found that with this technique
the protein content of the expiant during the first 18 h of incubation
was almost as great as in the developing egg, provided that the concentration of yolk-albumen was high in the medium and that a large
amount of area opaca was left attached to the embryo.
With all these techniques, development tends to be somewhat slower
than in ovo especially when the embryo is younger than the head process
stage at explantation. With older embryos, differentiation is often as
rapid as in ovo and the proportion of successful expiants is higher. If the
embryo fails to establish a circulation it dies, presumably because the
intracellular yolk stores of the area pellucida have all been utilized
(see Section IV). Generally, however, the embryo dies some hours after
the area vasculosa has been established. I t is probable that death occurs
when the stocks of intracellular yolk in the area vasculosa have also
become exhausted.
Spratt (1949, 1950) used the explantation technique to study the
nutritional requirements of the chick, and found that although the
embryos rapidly degenerated in a non-nutrient Ringer solution, they
differentiated quite well if glucose was added to the medium. Other
carbohydrates could also support development, though none so effectively as glucose (see review by Spratt, 1956). The importance of glucose
has been confirmed by other workers (e.g. Schechtman and Taylor,
1949; Fraser, 1959). Its distribution in the developing egg has been
studied by van Deth (1963).
Spratt found, however, that the embryo developed best of all on a
medium containing yolk and albumen. Thus, it can be assumed that the
embryo normally extracts rather more from the egg nutrients at this
time than glucose or its equivalent. Since egg-white alone provides such
excellent results it may be that the egg-white provides a valuable source
of nutrients in the early stages. Similar results were obtained by
Hayashi and Herrmann (1959) though Harrison (1960) obtained just as
good results with a glucose-saline mixture, provided the head fold stage
had already been reached at explantation.
Other workers have used this technique to investigate the accumulation of protein and amino acids in embryos growing on synthetic media.
Klein et al. (1962) who estimated the net accumulation of both protein
nitrogen and DNA, concluded that the chick needs both leucine and
lysine, but not aspartic acid or proline.
Solomon (1957) has shown that if chick blastoderms are growing on a
synthetic medium which contains glucose as its sole carbon source, they
are capable of synthesizing RNA and DNA. He points out, however,
that the precursors of these materials are normally obtained from the
extra-embryonic yolk stores.
RUTH BELLAIRS
technique. Britt and Herrmann (1959) found that with this technique
the protein content of the expiant during the first 18 h of incubation
was almost as great as in the developing egg, provided that the concentration of yolk-albumen was high in the medium and that a large
amount of area opaca was left attached to the embryo.
With all these techniques, development tends to be somewhat slower
than in ovo especially when the embryo is younger than the head process
stage at explantation. With older embryos, differentiation is often as
rapid as in ovo and the proportion of successful expiants is higher. If the
embryo fails to establish a circulation it dies, presumably because the
intracellular yolk stores of the area pellucida have all been utilized
(see Section IV). Generally, however, the embryo dies some hours after
the area vasculosa has been established. I t is probable that death occurs
when the stocks of intracellular yolk in the area vasculosa have also
become exhausted.
Spratt (1949, 1950) used the explantation technique to study the
nutritional requirements of the chick, and found that although the
embryos rapidly degenerated in a non-nutrient Ringer solution, they
differentiated quite well if glucose was added to the medium. Other
carbohydrates could also support development, though none so effectively as glucose (see review by Spratt, 1956). The importance of glucose
has been confirmed by other workers (e.g. Schechtman and Taylor,
1949; Fraser, 1959). Its distribution in the developing egg has been
studied by van Deth (1963).
Spratt found, however, that the embryo developed best of all on a
medium containing yolk and albumen. Thus, it can be assumed that the
embryo normally extracts rather more from the egg nutrients at this
time than glucose or its equivalent. Since egg-white alone provides such
excellent results it may be that the egg-white provides a valuable source
of nutrients in the early stages. Similar results were obtained by
Hayashi and Herrmann (1959) though Harrison (1960) obtained just as
good results with a glucose-saline mixture, provided the head fold stage
had already been reached at explantation.
Other workers have used this technique to investigate the accumulation of protein and amino acids in embryos growing on synthetic media.
Klein et al. (1962) who estimated the net accumulation of both protein
nitrogen and DNA, concluded that the chick needs both leucine and
lysine, but not aspartic acid or proline.
Solomon (1957) has shown that if chick blastoderms are growing on a
synthetic medium which contains glucose as its sole carbon source, they
are capable of synthesizing RNA and DNA. He points out, however,
that the precursors of these materials are normally obtained from the
extra-embryonic yolk stores.