20
JANE Μ. OPPENHEIMER
(1952), whose complicated theory to account for regional differentiation
calls on two different actions, one succeeding the other in time, of chordamesodermal substrate on overlying cells.
Furthermore, individual differences between the layers have provided
the starting point for some of the recent chemical approaches towards
the solution of enigmas concerning induction which the old transplantation methods have thus far been inadequate to unriddle. Specifically,
the work currently attempting to identify the chemical substances involved in the production of regional differentiation in the amphibian
(Toivonen and Kuusi, 1948; Toivonen, 1949, 1950, 1951; Yamada, 1950;
Kuusi, 1951; Hayashi, 1956; Yamada and Takata, 1956) is a direct outgrowth of the demonstration by Chuang (1939) that the abnormal inductors evoking the differentiation of mesoderm may differ from those
responsible for the production of neural tissue. Thus the lively activity
now being pursued in this field, even though now carried out by means
of chemical analyses, is witness to the tremendous weight of influence not
only of the organizer and gradient concepts, but also to that of the authority of the older germ layer concept, from which at most a small
minority of contemporary investigators has been able completely to
emancipate itself.
The possibility has already been lightly touched upon that the concepts of the 19th century did not necessarily suffer in comparison with
those of the 20th so far as their dynamic qualities were concerned; and
the degree to which chemical analyses are in fact more dynamic than
other morphological descriptions is a moot question. In any case, it is
eminently certain that at the supracellular as well as the cellular level,
even the 19th century viewed the germ layers as highly dynamic entities and investigated their transformations as events succeeding one
another in time. The concepts of motion which dominated physical
science by the end of the 19th century were clearly reflected not only in
general biological but also in specifically embryological interpretation,
see Roux (1885a, p. 412):
"Dies wäre die descriptive Definition der vor uns liegenden
weiteren Aufgabe der Embryologie; kurz gefasst also: die vollkommene Beschreibung aller, auch der kleinsten Entwicklungsvorgänge
als Substanzbewegungen der Theile des Eies und der von ihm
aufgenommenen Theile bis zur vollen Entwicklung des Individuums,
gestützt auf die vollkommene Kenntnis der Anordnung und äusseren
Beschaffenheit jedes kleinsten Theilchens des befruchteten Eies:
eine 'Kinematik der Entwicklung/ wenn wir, wie wohl zu empfehlen
JANE Μ. OPPENHEIMER
(1952), whose complicated theory to account for regional differentiation
calls on two different actions, one succeeding the other in time, of chordamesodermal substrate on overlying cells.
Furthermore, individual differences between the layers have provided
the starting point for some of the recent chemical approaches towards
the solution of enigmas concerning induction which the old transplantation methods have thus far been inadequate to unriddle. Specifically,
the work currently attempting to identify the chemical substances involved in the production of regional differentiation in the amphibian
(Toivonen and Kuusi, 1948; Toivonen, 1949, 1950, 1951; Yamada, 1950;
Kuusi, 1951; Hayashi, 1956; Yamada and Takata, 1956) is a direct outgrowth of the demonstration by Chuang (1939) that the abnormal inductors evoking the differentiation of mesoderm may differ from those
responsible for the production of neural tissue. Thus the lively activity
now being pursued in this field, even though now carried out by means
of chemical analyses, is witness to the tremendous weight of influence not
only of the organizer and gradient concepts, but also to that of the authority of the older germ layer concept, from which at most a small
minority of contemporary investigators has been able completely to
emancipate itself.
The possibility has already been lightly touched upon that the concepts of the 19th century did not necessarily suffer in comparison with
those of the 20th so far as their dynamic qualities were concerned; and
the degree to which chemical analyses are in fact more dynamic than
other morphological descriptions is a moot question. In any case, it is
eminently certain that at the supracellular as well as the cellular level,
even the 19th century viewed the germ layers as highly dynamic entities and investigated their transformations as events succeeding one
another in time. The concepts of motion which dominated physical
science by the end of the 19th century were clearly reflected not only in
general biological but also in specifically embryological interpretation,
see Roux (1885a, p. 412):
"Dies wäre die descriptive Definition der vor uns liegenden
weiteren Aufgabe der Embryologie; kurz gefasst also: die vollkommene Beschreibung aller, auch der kleinsten Entwicklungsvorgänge
als Substanzbewegungen der Theile des Eies und der von ihm
aufgenommenen Theile bis zur vollen Entwicklung des Individuums,
gestützt auf die vollkommene Kenntnis der Anordnung und äusseren
Beschaffenheit jedes kleinsten Theilchens des befruchteten Eies:
eine 'Kinematik der Entwicklung/ wenn wir, wie wohl zu empfehlen