I.
PROBLEM OF THE ORGANIZER
17
area is characterized by demolition of proteins which lead to active
synthetic processes, while the ventral area is characterized by inhibition
of protein demolition. He has many data to suggest that the agent which
causes animalization acts by accelerating the demolition of proteins
within the cells, and the vegetalizing agent acts by inhibiting the
demolition. He is also of the opinion that a similar antagonistic relationship exists between acceleration and suppression of notochordal
development in amphibian embryos, so that animalizing agents tend
to accelerate and vegetalizing agents tend to suppress notochordal
development. In fact, the observations cited above of solation of the
endoplasm of amphibian cells after ammonia and thiocyanate treatments
which lead to dorsalization, and of suppression of solation under the
influence of sucrose and glucose which inhibit dorsalization, are in good
accord with the idea.
IV. Chemical Factors Operative in Heterogenous Induction
By inserting pieces of tissues from various animals into the blastocoel
of Triturus gastrulae, Holtfreter (1934) showed that the ability to
induce neural and mesodermal structures is present throughout the
animal kingdom. Subsequent studies along this line led Chuang (1939,
1940) and Toivonen (1940) to the important discovery that various
tissues of various animals bring forth inductions which are regionally
specific. In most cases the specificity was found to be stable toward
ethanol treatment of the tissues. An array of structures belonging to one
or two embryonic regions is formed under the influence of one of these
tissues. Taken together, these tissues give rise to almost all the principal
structures of the three germ layers from the presumptive ectoderm of
Triturus gastrulae (Table I). No definite correlation exists, however,
between the embryological source of the tissue used as the inductor and
the regional effect of the tissue on the ectoderm. It has been well
established that various parts of the organizer exert regionally specific
inductive effects on the ectoderm. Thus, the anterior, middle, and the
posterior zones of the archenteric roof of Triturus neurulae induce in
the living condition preferentially archencephalic, deuterencephalic, and
spino-caudal structures respectively (Mangold, 1933; Ter Horst, 1948).
Comparing regional effects of the heterogenous inductor with those of
the normal organizer, it was argued that studies of chemical factors of
heterogenous inductors may clarify the chemical mechanism underlying
the normal induction by the organizer. Although some doubt exists
about the validity of the argument (Section V), it is certainly an
important task to establish what chemical and physical factors are
responsible for causing specific differentiations in one and the same
reaction system.
PROBLEM OF THE ORGANIZER
17
area is characterized by demolition of proteins which lead to active
synthetic processes, while the ventral area is characterized by inhibition
of protein demolition. He has many data to suggest that the agent which
causes animalization acts by accelerating the demolition of proteins
within the cells, and the vegetalizing agent acts by inhibiting the
demolition. He is also of the opinion that a similar antagonistic relationship exists between acceleration and suppression of notochordal
development in amphibian embryos, so that animalizing agents tend
to accelerate and vegetalizing agents tend to suppress notochordal
development. In fact, the observations cited above of solation of the
endoplasm of amphibian cells after ammonia and thiocyanate treatments
which lead to dorsalization, and of suppression of solation under the
influence of sucrose and glucose which inhibit dorsalization, are in good
accord with the idea.
IV. Chemical Factors Operative in Heterogenous Induction
By inserting pieces of tissues from various animals into the blastocoel
of Triturus gastrulae, Holtfreter (1934) showed that the ability to
induce neural and mesodermal structures is present throughout the
animal kingdom. Subsequent studies along this line led Chuang (1939,
1940) and Toivonen (1940) to the important discovery that various
tissues of various animals bring forth inductions which are regionally
specific. In most cases the specificity was found to be stable toward
ethanol treatment of the tissues. An array of structures belonging to one
or two embryonic regions is formed under the influence of one of these
tissues. Taken together, these tissues give rise to almost all the principal
structures of the three germ layers from the presumptive ectoderm of
Triturus gastrulae (Table I). No definite correlation exists, however,
between the embryological source of the tissue used as the inductor and
the regional effect of the tissue on the ectoderm. It has been well
established that various parts of the organizer exert regionally specific
inductive effects on the ectoderm. Thus, the anterior, middle, and the
posterior zones of the archenteric roof of Triturus neurulae induce in
the living condition preferentially archencephalic, deuterencephalic, and
spino-caudal structures respectively (Mangold, 1933; Ter Horst, 1948).
Comparing regional effects of the heterogenous inductor with those of
the normal organizer, it was argued that studies of chemical factors of
heterogenous inductors may clarify the chemical mechanism underlying
the normal induction by the organizer. Although some doubt exists
about the validity of the argument (Section V), it is certainly an
important task to establish what chemical and physical factors are
responsible for causing specific differentiations in one and the same
reaction system.