208
GEORGE SZÉKELY
the normal limbs of newly hatched chickens; therefore, if the reflexes had
been the result of specific synaptic connections of the graft-innervating
nerves developed during the embryonic life, they should have been evoked
also from the graft promptly after hatching. However, the appearance,
especially that of the complex responses, was retarded, and their gradual
emergence suggested that a kind of functional mechanism was at work
rather than actual establishment of new anatomical connections. Furthermore, if the nerves were specified by the grafts, there should have been
a difference in the responses evoked from a wing or from a leg, but no
such differences were found. A thorough analysis of the observations may
suggest an interpretation from another point of view.
Especially interesting in this respect is the observed dissociation of
pain sensation and the specific reflexogenic capacity of the graft in
evoking simple reflexes, on the one hand, and, on the other hand, the
observation that complex responses were evoked only from pain-sensitive points. This may mean that pain sensitivity of the graft was not
essential to evoke a simple reflex, but a painful stimulation was apparently necessary for complex responses. Another finding is that only
simple reflexes could be elicited from grafts supplied mainly by a single
segmental nerve, whereas the complex responses have all been obtained
from grafts with multisegmental innervation and plexus formation between the supplying nerves. These two observations suggest that the
nature of the responses depends on some physiological characteristics
(different sensation qualities, number of activated fibers, the intermingling of fibers from different segments) of the afferent impulses. In other
words, the complex impulse which is fed in from a graft may be quite
different from that from the adjacent skin and may be similar to that
from a normal limb. It is assumed, furthermore that the central nervous
system is capable of discriminating between impulses from limbs and
from the surrounding skin and dispatching them toward appropriate
centers.
The question immediately arises whether the spinal cord can possess
such a complex system for the analysis of different impulse patterns and
their dispatch toward different loci without the formation of specific
anatomical pathways. In a histological study of the cat's spinal cord,
Szentâgothai (1964) has shown the exquisite complexity of the substantia gelatinosa, the main input mechanism for nociceptive impulses.
Unfortunately, shortage of space prevents a detailed description of these
remarkable findings, but it is enough to mention that the structure of the
substantia gelatinosa closely resembles that of the cerebellar cortex. The
substantia itself is a self-contained neuron system, all axons of which
GEORGE SZÉKELY
the normal limbs of newly hatched chickens; therefore, if the reflexes had
been the result of specific synaptic connections of the graft-innervating
nerves developed during the embryonic life, they should have been evoked
also from the graft promptly after hatching. However, the appearance,
especially that of the complex responses, was retarded, and their gradual
emergence suggested that a kind of functional mechanism was at work
rather than actual establishment of new anatomical connections. Furthermore, if the nerves were specified by the grafts, there should have been
a difference in the responses evoked from a wing or from a leg, but no
such differences were found. A thorough analysis of the observations may
suggest an interpretation from another point of view.
Especially interesting in this respect is the observed dissociation of
pain sensation and the specific reflexogenic capacity of the graft in
evoking simple reflexes, on the one hand, and, on the other hand, the
observation that complex responses were evoked only from pain-sensitive points. This may mean that pain sensitivity of the graft was not
essential to evoke a simple reflex, but a painful stimulation was apparently necessary for complex responses. Another finding is that only
simple reflexes could be elicited from grafts supplied mainly by a single
segmental nerve, whereas the complex responses have all been obtained
from grafts with multisegmental innervation and plexus formation between the supplying nerves. These two observations suggest that the
nature of the responses depends on some physiological characteristics
(different sensation qualities, number of activated fibers, the intermingling of fibers from different segments) of the afferent impulses. In other
words, the complex impulse which is fed in from a graft may be quite
different from that from the adjacent skin and may be similar to that
from a normal limb. It is assumed, furthermore that the central nervous
system is capable of discriminating between impulses from limbs and
from the surrounding skin and dispatching them toward appropriate
centers.
The question immediately arises whether the spinal cord can possess
such a complex system for the analysis of different impulse patterns and
their dispatch toward different loci without the formation of specific
anatomical pathways. In a histological study of the cat's spinal cord,
Szentâgothai (1964) has shown the exquisite complexity of the substantia gelatinosa, the main input mechanism for nociceptive impulses.
Unfortunately, shortage of space prevents a detailed description of these
remarkable findings, but it is enough to mention that the structure of the
substantia gelatinosa closely resembles that of the cerebellar cortex. The
substantia itself is a self-contained neuron system, all axons of which