15. E M B R Y O G E N E S I S in vitro
545
of deuterencephalic or spinal type, never of archencephalic type.
It may be concluded from these results that the induction of different
neural formations, pigmentary and mesodermal tissues, is not necessarily tied to either live tissues or solid substances, but that it can be
produced by substances in solution or in suspension in a liquid medium.
(b) Other authors propose, on the contrary, that the inducing effect
is a surface action of the antigen-antibody type (P. Weiss, 1949).
According to this hypothesis, connexions are established between the
molecules of the inducer and those of the responsive tissue in the manner
of a lock-and-key system. At the interface between these two tissues, the
molecules of the inducer surface would become attached to the molecules of the responsive tissue which they would modify in a permanent
manner. Let us note that this explanation is not incompatible with the
existence of diffusible inducing substances. One of the most recent
attempts to verify this hypothesis was made by Vainio (1957). If an
antigen-antibody type of action does exist between the inducer and the
reacting substance, one should be able to inactivate the inducing
power of a tissue by the addition of antisera prepared in rabbits. The
author worked on heterologous inducers, probably of protein nature,
and whose effects are specific: they were guinea-pig liver, kidney and
bone marrow. After treatment with the anti-sera, corresponding
respectively to these tissues, the inducing effect of the marrow and the
kidney was strongly inhibited; that of the liver was inhibited too,
but at the same time it was modified. Normally, it induces archencephalon; after treatment by the anti-liver antiserum, it became a
mesodermal inducer. The control serum did not weaken the inducing
power of these tissues. Guinea-pig marrow and liver treated with the
anti-serum to the dorsal lip of the blastopore of the gastrula of Triton
were inactivated or weakened: the archencephalic inducer from liver
was transformed into a mesodermal inducer, as in the previous experiment.
There is no contradiction between these two explanations. A diffusible substance can exercise its influence by surface actions at the level
of the molecules of the responsive tissue.
D. SPECIFIC A C T I O N OF C E R T A I N A R T I F I C I A L I N D U C E R S
The problem regarding the nature of the primary inducer emerged
from the rut in which it had been stuck on the day when it was shown
that artificial inducers could have specific, precise and constant effects.
Chuang (1938) and Toivonen (1940) were the first to show that
certain organs, such as the liver of Triton, the kidney of guinea-pig, and
the kidney of perch, primarily induce the organs of the trunk or of the
T
545
of deuterencephalic or spinal type, never of archencephalic type.
It may be concluded from these results that the induction of different
neural formations, pigmentary and mesodermal tissues, is not necessarily tied to either live tissues or solid substances, but that it can be
produced by substances in solution or in suspension in a liquid medium.
(b) Other authors propose, on the contrary, that the inducing effect
is a surface action of the antigen-antibody type (P. Weiss, 1949).
According to this hypothesis, connexions are established between the
molecules of the inducer and those of the responsive tissue in the manner
of a lock-and-key system. At the interface between these two tissues, the
molecules of the inducer surface would become attached to the molecules of the responsive tissue which they would modify in a permanent
manner. Let us note that this explanation is not incompatible with the
existence of diffusible inducing substances. One of the most recent
attempts to verify this hypothesis was made by Vainio (1957). If an
antigen-antibody type of action does exist between the inducer and the
reacting substance, one should be able to inactivate the inducing
power of a tissue by the addition of antisera prepared in rabbits. The
author worked on heterologous inducers, probably of protein nature,
and whose effects are specific: they were guinea-pig liver, kidney and
bone marrow. After treatment with the anti-sera, corresponding
respectively to these tissues, the inducing effect of the marrow and the
kidney was strongly inhibited; that of the liver was inhibited too,
but at the same time it was modified. Normally, it induces archencephalon; after treatment by the anti-liver antiserum, it became a
mesodermal inducer. The control serum did not weaken the inducing
power of these tissues. Guinea-pig marrow and liver treated with the
anti-serum to the dorsal lip of the blastopore of the gastrula of Triton
were inactivated or weakened: the archencephalic inducer from liver
was transformed into a mesodermal inducer, as in the previous experiment.
There is no contradiction between these two explanations. A diffusible substance can exercise its influence by surface actions at the level
of the molecules of the responsive tissue.
D. SPECIFIC A C T I O N OF C E R T A I N A R T I F I C I A L I N D U C E R S
The problem regarding the nature of the primary inducer emerged
from the rut in which it had been stuck on the day when it was shown
that artificial inducers could have specific, precise and constant effects.
Chuang (1938) and Toivonen (1940) were the first to show that
certain organs, such as the liver of Triton, the kidney of guinea-pig, and
the kidney of perch, primarily induce the organs of the trunk or of the
T