180
F. Ε. LEHMANN
Β. Growth as a Process Integrated in Space and in Time
The detailed investigation of regeneration in Xenopus demonstrates
that formation and growth of regenerates is an intricately interwoven
synergistic action of several biological processes. The amputation is
immediately followed by the wound period in which the activation of
migrating tissue cells begins very rapidly. With the closure of the wound
(8-10 hours after amputation) by mobile cells, the traumatic phase
comes to an end and the phase of cell migration and blastema formation
begins. The cells next to the amputation surface are activated to a
depth of 1 mm and furnish cells which build the blastemas and are
tissue specific for the different organs of the regenerate. The regenerate
which is now 72 hours old is sharply delimited with its undifferentiated
blastema cells from the histologically differentiated tissues of the stump.
The blastema formation culminates at the end of the 3rd and the
beginning of the 4th day. During this period numerous mitoses appear,
first in the stump and later in the blastema of the regenerate. Between
the 5th and the 10th day the histological differentiation is accomplished
and the morphological transformation of the regenerate and the stump
into the definite tail takes place in a harmonious way.
Our experiments with different pairs of morphostatic substances
suggested the hypothesis that one of the partner substances modifies
one partial process which starts early whereas a second partial process
which begins later is influenced by the second partner. This hypothesis
included the assumption that the single morphostatic substances were
not unspecifically inhibitory but that each morphostatic substance
modified only some restricted partial process and showed therefore a
kind of phase specificity. The combination of the different action
patterns should therefore produce a very broad synergistic effect in the
sense of Veldstra (1956) or a 'kombinative Einheitsleistung' in the sense
of Lehmann (1933, 1945).
Our hypothesis can be tested by determining the reaction of a
regeneration process to a reduced duration of treatment. This abbreviated
treatment might be applied to any sensitive phase either at the beginning
or at a late phase of regeneration. All of our experiments with eggs of
Tubifex or with regenerating tails of Xenopus show that an abbreviated
or
e
shock
5 treatment with one inhibitor substance can be nearly as
efficient as a treatment which includes the whole duration of regeneration. It becomes clear from these experiments that the peaks of
sensitivity are located in different phases. (Lehmann and Bretscher, 1952;
Lehmann, 1957b). We can conclude from our previous experiments that
further morphostatic substances can be found which act specifically
upon given phases and processes of regeneration. But the finding of
F. Ε. LEHMANN
Β. Growth as a Process Integrated in Space and in Time
The detailed investigation of regeneration in Xenopus demonstrates
that formation and growth of regenerates is an intricately interwoven
synergistic action of several biological processes. The amputation is
immediately followed by the wound period in which the activation of
migrating tissue cells begins very rapidly. With the closure of the wound
(8-10 hours after amputation) by mobile cells, the traumatic phase
comes to an end and the phase of cell migration and blastema formation
begins. The cells next to the amputation surface are activated to a
depth of 1 mm and furnish cells which build the blastemas and are
tissue specific for the different organs of the regenerate. The regenerate
which is now 72 hours old is sharply delimited with its undifferentiated
blastema cells from the histologically differentiated tissues of the stump.
The blastema formation culminates at the end of the 3rd and the
beginning of the 4th day. During this period numerous mitoses appear,
first in the stump and later in the blastema of the regenerate. Between
the 5th and the 10th day the histological differentiation is accomplished
and the morphological transformation of the regenerate and the stump
into the definite tail takes place in a harmonious way.
Our experiments with different pairs of morphostatic substances
suggested the hypothesis that one of the partner substances modifies
one partial process which starts early whereas a second partial process
which begins later is influenced by the second partner. This hypothesis
included the assumption that the single morphostatic substances were
not unspecifically inhibitory but that each morphostatic substance
modified only some restricted partial process and showed therefore a
kind of phase specificity. The combination of the different action
patterns should therefore produce a very broad synergistic effect in the
sense of Veldstra (1956) or a 'kombinative Einheitsleistung' in the sense
of Lehmann (1933, 1945).
Our hypothesis can be tested by determining the reaction of a
regeneration process to a reduced duration of treatment. This abbreviated
treatment might be applied to any sensitive phase either at the beginning
or at a late phase of regeneration. All of our experiments with eggs of
Tubifex or with regenerating tails of Xenopus show that an abbreviated
or
e
shock
5 treatment with one inhibitor substance can be nearly as
efficient as a treatment which includes the whole duration of regeneration. It becomes clear from these experiments that the peaks of
sensitivity are located in different phases. (Lehmann and Bretscher, 1952;
Lehmann, 1957b). We can conclude from our previous experiments that
further morphostatic substances can be found which act specifically
upon given phases and processes of regeneration. But the finding of