TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
13
direction of the more modern work than its components, the organizer
and gradient concepts, and it is a distinction of both of these that they
have each directly stimulated the study of morphogenetic phenomena on
other than a cellular level. The work on abnormal inductors carried out
in Spemann's laboratory and by Holtfreter in Dahlem was one of the
principal factors responsible for turning embryology directly toward its
present chemical phase. Child's theories had a similar effect by virtue of
their emphasis, new in their time, on the metabolic basis of differentiation; and in fact, it has proved highly significant that this was expressed
by Child in terms of the utilization of oxygen. From this point of view,
even though vertebrate embryologists have found the concepts of Spemann more compatible to elucidation of what is known of vertebrate
development, the work of Child has been of inestimable general influence.
It was Child who first systematically applied the methods of general
physiology to the study of morphogenesis. The program of J. Loeb
(1905), who was also treating the egg and embryo as a physico-chemical
system, was like that of so many of his embryological contemporaries at
the turn of the century far more varied and variable. Although repetition
of Child's experiments by techniques more critical than poisoning an
organism by cyanide failed to confirm his results, and while Warburg's
studies in 1908 and 1910 on respiration in the sea urchin egg were other
contributing factors, it seems safe to say that the wide dissemination, in
doctrinaire tone, of Child's generalizations among biological investigators at least accelerated, if in fact it did not do more, the progress of
the more accurate and more fruitful studies on respiratory systems within
the egg which were to be performed by Brächet (1934), Boell et al.
(1939) and the many others who have carried these investigations farther
(Boell, 1955). Needham (1942, p. 605), himself an interested party of
the top rank in this connection, believes too that
. . it is sure that embryology owes a considerable debt to Child,
who by introducing his gradient concept was one of the first to
recognize those invisible dispositions of order with which the organism imposes its organization on the matter of which it is made. Today the gradient theory has merged in the general theory of
morphogenetic fields, already discussed. ... It is not likely we
shall be able to do without this in the future progress of embryology."
Furthermore, it cannot be denied that for some particular organisms
the existence of gradients has not only been confirmed but demonstrably
13
direction of the more modern work than its components, the organizer
and gradient concepts, and it is a distinction of both of these that they
have each directly stimulated the study of morphogenetic phenomena on
other than a cellular level. The work on abnormal inductors carried out
in Spemann's laboratory and by Holtfreter in Dahlem was one of the
principal factors responsible for turning embryology directly toward its
present chemical phase. Child's theories had a similar effect by virtue of
their emphasis, new in their time, on the metabolic basis of differentiation; and in fact, it has proved highly significant that this was expressed
by Child in terms of the utilization of oxygen. From this point of view,
even though vertebrate embryologists have found the concepts of Spemann more compatible to elucidation of what is known of vertebrate
development, the work of Child has been of inestimable general influence.
It was Child who first systematically applied the methods of general
physiology to the study of morphogenesis. The program of J. Loeb
(1905), who was also treating the egg and embryo as a physico-chemical
system, was like that of so many of his embryological contemporaries at
the turn of the century far more varied and variable. Although repetition
of Child's experiments by techniques more critical than poisoning an
organism by cyanide failed to confirm his results, and while Warburg's
studies in 1908 and 1910 on respiration in the sea urchin egg were other
contributing factors, it seems safe to say that the wide dissemination, in
doctrinaire tone, of Child's generalizations among biological investigators at least accelerated, if in fact it did not do more, the progress of
the more accurate and more fruitful studies on respiratory systems within
the egg which were to be performed by Brächet (1934), Boell et al.
(1939) and the many others who have carried these investigations farther
(Boell, 1955). Needham (1942, p. 605), himself an interested party of
the top rank in this connection, believes too that
. . it is sure that embryology owes a considerable debt to Child,
who by introducing his gradient concept was one of the first to
recognize those invisible dispositions of order with which the organism imposes its organization on the matter of which it is made. Today the gradient theory has merged in the general theory of
morphogenetic fields, already discussed. ... It is not likely we
shall be able to do without this in the future progress of embryology."
Furthermore, it cannot be denied that for some particular organisms
the existence of gradients has not only been confirmed but demonstrably