28
TUNEO
YAMADA
brief account of which will be given in this section. Before we discuss
the experiments, it is perhaps convenient to make clear the difference
which exists between the inducing agents of the heterogenous inductors
and that of the living organizer. As pointed out in the foregoing section,
in the case of heterogenous inductors of birds and mammals, all regional
types of induction are more or less stable toward ethanol treatment of
relatively short duration. This is unlike the induction by tissues of the
Amphibia (spino-caudal induction by Triturus liver, and trunkmesodermal induction by Rana skin) which seems to be characterized
by instability toward treatment with ethanol at room temperature
(Yamada, unpublished work).In the case of the amphibian organizer, the
situation is somewhat complex. Several years after the discovery of the
organizer, Bautzmann (1932), Wehmeier (c/. Spemann, 1932) and
Holtfreter (1933b) found that after heating, drying, freezing, and
ethanol treatment, the dorsal lip and neural plate of amphibian
embryos are capable of evoking neural differentiation in competent
ectoderm. With the sandwich method Holtfreter (1933b) gave a
beautiful demonstration of the inducing ability of the 'dead organizer'.
Simultaneously it was established by him that heating or ethanol
treatment endows with inducing ability those embryonic areas which do
not induce in the living condition. Now what appears important is that
the induction caused by killed embryonic areas always falls either into
the archencephalic or into the indifferent neural type, and in this sense,
is comparable with the differentiation of the ectoderm after treatment
with injurious agents (Section III). Thus the embryonic areas having
deuterencephalic or spino-caudal effects during life, cause formation of
archencephalic or indifferent neural structures after ethanol or heat
treatment, as was shown clearly in the sandwich experiments by
Rollhäuser (1953). She emphasized the idea that through denaturation
all the original inducing agents of the normal induction disappear, and,
at the same time in all embryonic areas, a new substance appears
which causes only archencephalic induction. Okazaki (1955) working in
our laboratory showed that when the neural plate of Triturus pyrrhogaster was devitalized with mild treatment such as exposure to ethanol
at -18°C, freezing-drying, and freezing-thawing, it induced archencephalic structures at a very low frequency. When, however, the neural
plate treated in this way was further treated with ethanol at 5° C, a high
frequency of archencephalic induction was obtained. Reversal of the
order of the double treatment gave the same results. Okazaki interpreted
the results as suggesting that the devitalization, as such, deprives the
organizer of its original inducing capacity, and that denaturation of
proteins caused by treating with ethanol at 5° C evokes in the embryonic
cells a new capacity for archencephalic induction. In this connection it
TUNEO
YAMADA
brief account of which will be given in this section. Before we discuss
the experiments, it is perhaps convenient to make clear the difference
which exists between the inducing agents of the heterogenous inductors
and that of the living organizer. As pointed out in the foregoing section,
in the case of heterogenous inductors of birds and mammals, all regional
types of induction are more or less stable toward ethanol treatment of
relatively short duration. This is unlike the induction by tissues of the
Amphibia (spino-caudal induction by Triturus liver, and trunkmesodermal induction by Rana skin) which seems to be characterized
by instability toward treatment with ethanol at room temperature
(Yamada, unpublished work).In the case of the amphibian organizer, the
situation is somewhat complex. Several years after the discovery of the
organizer, Bautzmann (1932), Wehmeier (c/. Spemann, 1932) and
Holtfreter (1933b) found that after heating, drying, freezing, and
ethanol treatment, the dorsal lip and neural plate of amphibian
embryos are capable of evoking neural differentiation in competent
ectoderm. With the sandwich method Holtfreter (1933b) gave a
beautiful demonstration of the inducing ability of the 'dead organizer'.
Simultaneously it was established by him that heating or ethanol
treatment endows with inducing ability those embryonic areas which do
not induce in the living condition. Now what appears important is that
the induction caused by killed embryonic areas always falls either into
the archencephalic or into the indifferent neural type, and in this sense,
is comparable with the differentiation of the ectoderm after treatment
with injurious agents (Section III). Thus the embryonic areas having
deuterencephalic or spino-caudal effects during life, cause formation of
archencephalic or indifferent neural structures after ethanol or heat
treatment, as was shown clearly in the sandwich experiments by
Rollhäuser (1953). She emphasized the idea that through denaturation
all the original inducing agents of the normal induction disappear, and,
at the same time in all embryonic areas, a new substance appears
which causes only archencephalic induction. Okazaki (1955) working in
our laboratory showed that when the neural plate of Triturus pyrrhogaster was devitalized with mild treatment such as exposure to ethanol
at -18°C, freezing-drying, and freezing-thawing, it induced archencephalic structures at a very low frequency. When, however, the neural
plate treated in this way was further treated with ethanol at 5° C, a high
frequency of archencephalic induction was obtained. Reversal of the
order of the double treatment gave the same results. Okazaki interpreted
the results as suggesting that the devitalization, as such, deprives the
organizer of its original inducing capacity, and that denaturation of
proteins caused by treating with ethanol at 5° C evokes in the embryonic
cells a new capacity for archencephalic induction. In this connection it