TWENTIETH CENTURY EMBRYOLOGICAL CONCEPTS
17
modern embryology. The specific results of these experiments, fascinating in their own right, were important also in that they provided a firm
and concrete foundation for the concept of fields. His own interpretations were of no less significance in that they were expressed in terms
of spatial transformations in time, and they were timely in their attempts
to refer both gross and subtle morphogenetic effects to molecular
phenomena: a mere analogy to the tetrahedral carbon atom in 1921 was
followed in 1936 by a "conclusion that the transformation from the first
to the second phase [in the step-wise differentiation of asymmetry] and
probably, in some measure at least, that from the second to the third
phase involve changes in the orientation of ultramicroscopic elements"
(Harrison, 1936, p. 246). The ultramicroscopic elements were revealed
in the Harvard Tercentenary Address (delivered as a lecture in 1936;
published 1945) as none other than protein molecules, whose arrangement could be postulated as accounting for a number of polar and
other phenomena.
This hypothesis was however at most a modest and tentative one
which was never aggrandized to a comprehensive theory. In fact, in his
avoidance of general theorizing in favor of investigation of a wide variety
of developmental phenomena Harrison's mind has exemplified the
vigorously progressive tendencies distinctive of the beginning of the
century. In his own work he dealt specifically with material as widely
divergent as the outgrowing axone, the medullary plate, the lens, the
lateral line, the ear, the fin, the limb, and the manifold derivatives of
the neural crest. While he confined his own efforts, after the very first,
to the amphibian, experimental investigations on fish and mammal were
pursued in his laboratory at the instigation of Nicholas (1927, 1934), and
scarcely an organ or organ system has escaped investigation in his laboratory or by its members (see, for instance, for the range of material
covered, and the varied nature of the particular problems attacked, the
tables of contents of the Festschrift volumes 113 (1950) and 129 (1955)
of the Journal of Experimental
Zoology).
These investigations have provided fundamental data which, while they have answered some of the
familiar questions of the past, have in the main raised new ones to be
solved by the future. If they have been constructed principally in terms
of organs or organ-systems, this serves only to emphasize the fact that
these too, like the whole embryo, function on a high plane of integration.
17
modern embryology. The specific results of these experiments, fascinating in their own right, were important also in that they provided a firm
and concrete foundation for the concept of fields. His own interpretations were of no less significance in that they were expressed in terms
of spatial transformations in time, and they were timely in their attempts
to refer both gross and subtle morphogenetic effects to molecular
phenomena: a mere analogy to the tetrahedral carbon atom in 1921 was
followed in 1936 by a "conclusion that the transformation from the first
to the second phase [in the step-wise differentiation of asymmetry] and
probably, in some measure at least, that from the second to the third
phase involve changes in the orientation of ultramicroscopic elements"
(Harrison, 1936, p. 246). The ultramicroscopic elements were revealed
in the Harvard Tercentenary Address (delivered as a lecture in 1936;
published 1945) as none other than protein molecules, whose arrangement could be postulated as accounting for a number of polar and
other phenomena.
This hypothesis was however at most a modest and tentative one
which was never aggrandized to a comprehensive theory. In fact, in his
avoidance of general theorizing in favor of investigation of a wide variety
of developmental phenomena Harrison's mind has exemplified the
vigorously progressive tendencies distinctive of the beginning of the
century. In his own work he dealt specifically with material as widely
divergent as the outgrowing axone, the medullary plate, the lens, the
lateral line, the ear, the fin, the limb, and the manifold derivatives of
the neural crest. While he confined his own efforts, after the very first,
to the amphibian, experimental investigations on fish and mammal were
pursued in his laboratory at the instigation of Nicholas (1927, 1934), and
scarcely an organ or organ system has escaped investigation in his laboratory or by its members (see, for instance, for the range of material
covered, and the varied nature of the particular problems attacked, the
tables of contents of the Festschrift volumes 113 (1950) and 129 (1955)
of the Journal of Experimental
Zoology).
These investigations have provided fundamental data which, while they have answered some of the
familiar questions of the past, have in the main raised new ones to be
solved by the future. If they have been constructed principally in terms
of organs or organ-systems, this serves only to emphasize the fact that
these too, like the whole embryo, function on a high plane of integration.