15. E M B R Y O G E N E S I S in vitro
553
The authors considered that the rate of dialysis was too slow for the
active substance to be a polypeptide and that it is likely on these
grounds also to be a more complex protein.
Though it is now clear that the substances inducing archencephalic
and deuterencephalic formations, though linked to nucleoprotein
fractions, are not the nucleic acids (RNA and D N A ) , but rather the
associated proteins, a final problem remains. D o the proteins of specific
inducers differ from each other in a fundamental and intrinsic manner?
The fact that one can pass from one to the other with the aid of temperature changes or of chemical agents makes it a likely supposition
that we are dealing with the same molecule subjected to different
degrees of transformation. Yamada's (1959) investigations, showing
the progressive change from the mesodermal to the archencephalic
type, through spino-caudal and deuterencephalic stages, speak in
favour of this hypothesis. Hayashi (1958) thinks that the two functions—
mesodermizing and neuralizing—could co-exist in the same molecule,
one representing an unstable, the other a stable state of the inducing
proteins. Only a more precise biochemical analysis will make possible
the solution of this problem.
I I . IN VITRO
C U L T U R E OF E M B R Y O S OF B I R D S
In vitro culture of avian blastoderms has opened two fields of research:
(1) research into experimental morphogenesis in cases where experimentation in ovo is completely blocked by difficulties, and (2) research
into the metabolic needs of the embryo and its organs, and into the
factors stimulating and inhibiting morphogenesis and growth.
A. M E T H O D S
The methods all aim at separating the blastoderm from the enormous
mass of the extracellular yolk of chick egg and of spreading it out on
a solid nutritive milieu. Waddington (1932) was the first to adapt
Fell's technique of organ culture to the explantation of young blastoderms. He used a coagulum of chick plasma and embryo juice. The
medium was prepared in a watch glass which was kept in a moist
chamber throughout the duration of the culture.
Spratt (1947) used for substrate a gel of agar in physiological salt
solution, to which he added a nutritive medium composed of an
extract of the white and the yolk of egg, or of albumin alone. In further
experiments, Spratt (1948) prepared synthetic media in which natural
foods were replaced by a mixture of amino acids, sugars, and vitamins,
T*
553
The authors considered that the rate of dialysis was too slow for the
active substance to be a polypeptide and that it is likely on these
grounds also to be a more complex protein.
Though it is now clear that the substances inducing archencephalic
and deuterencephalic formations, though linked to nucleoprotein
fractions, are not the nucleic acids (RNA and D N A ) , but rather the
associated proteins, a final problem remains. D o the proteins of specific
inducers differ from each other in a fundamental and intrinsic manner?
The fact that one can pass from one to the other with the aid of temperature changes or of chemical agents makes it a likely supposition
that we are dealing with the same molecule subjected to different
degrees of transformation. Yamada's (1959) investigations, showing
the progressive change from the mesodermal to the archencephalic
type, through spino-caudal and deuterencephalic stages, speak in
favour of this hypothesis. Hayashi (1958) thinks that the two functions—
mesodermizing and neuralizing—could co-exist in the same molecule,
one representing an unstable, the other a stable state of the inducing
proteins. Only a more precise biochemical analysis will make possible
the solution of this problem.
I I . IN VITRO
C U L T U R E OF E M B R Y O S OF B I R D S
In vitro culture of avian blastoderms has opened two fields of research:
(1) research into experimental morphogenesis in cases where experimentation in ovo is completely blocked by difficulties, and (2) research
into the metabolic needs of the embryo and its organs, and into the
factors stimulating and inhibiting morphogenesis and growth.
A. M E T H O D S
The methods all aim at separating the blastoderm from the enormous
mass of the extracellular yolk of chick egg and of spreading it out on
a solid nutritive milieu. Waddington (1932) was the first to adapt
Fell's technique of organ culture to the explantation of young blastoderms. He used a coagulum of chick plasma and embryo juice. The
medium was prepared in a watch glass which was kept in a moist
chamber throughout the duration of the culture.
Spratt (1947) used for substrate a gel of agar in physiological salt
solution, to which he added a nutritive medium composed of an
extract of the white and the yolk of egg, or of albumin alone. In further
experiments, Spratt (1948) prepared synthetic media in which natural
foods were replaced by a mixture of amino acids, sugars, and vitamins,
T*