110
R. J.
GOSS
A. Initial Stimulus
Regeneration does not occur spontaneously. When the normal
balance of parts is disturbed, however, regeneration may bring about
the restoration of missing structures. The most common stimulus to
regeneration is amputation, whereupon a straightforward replacement
of the lost parts ensues. Under these conditions regeneration can occur
only if part of an extremity is removed, for if the entire structure is
ablated there is left behind no source of materials from which a new
outgrowth can be produced. Thus, in initiating regeneration, it is
essential to understand the limits of the territory capable of participating
in renewed development.
Other types of injuries, short of complete amputation, can also stimulate the process of regeneration. It is not necessary to remove a mass
of tissue which is to be replaced, for the mere absence of parts is apparently not an important aspect of appendage regeneration initiation (in
contrast to Wolffian regeneration of the urodele lens, and the restitution of certain internal organs). The principal stimulus for appendage
regeneration appears to be injury, nor does it seem to make much
difference what the nature of the trauma may be. Regenerative growth
has been observed as a result of ligation of limbs, the transplantation of
living or devitalized tissues under the skin, the subcutaneous implantation of carcinogenic substances, exposure to ultra-violet irradiation,
and deviation of nerves to wounded regions. It has been occasionally
claimed that some of these treatments act in specific ways to bring about
regeneration, but in view of the diversity of such successful methods it
would appear likely that nonspecific injury may be the stimulus common
to most. Whatever the method of induction, regeneration under these
circumstances results in the production of supernumerary outgrowths.
The kind of structure formed is entirely dependent upon its location and
characteristic of the appendage being replaced. This cellular differentiation proceeds in a remarkably orderly way, each tissue developing in
precisely the correct position in continuity with the corresponding tissue
in the stump. Concomitant with the proximo-distally directed differentiation, the entire structural pattern of the regenerate takes shape,
reflecting the operation of morphogenetic influences. The latter somehow direct the spatial organization of the competent tissues, are responsible for the general orientation of the regenerate and ensure the production of a whole, well-integrated appendage. The aforementioned
processes, to be considered below in greater detail, all occur in a temporally and spatially co-ordinated sequence culminating ultimately in
the cessation of growth once a complete regenerate has been produced.
R. J.
GOSS
A. Initial Stimulus
Regeneration does not occur spontaneously. When the normal
balance of parts is disturbed, however, regeneration may bring about
the restoration of missing structures. The most common stimulus to
regeneration is amputation, whereupon a straightforward replacement
of the lost parts ensues. Under these conditions regeneration can occur
only if part of an extremity is removed, for if the entire structure is
ablated there is left behind no source of materials from which a new
outgrowth can be produced. Thus, in initiating regeneration, it is
essential to understand the limits of the territory capable of participating
in renewed development.
Other types of injuries, short of complete amputation, can also stimulate the process of regeneration. It is not necessary to remove a mass
of tissue which is to be replaced, for the mere absence of parts is apparently not an important aspect of appendage regeneration initiation (in
contrast to Wolffian regeneration of the urodele lens, and the restitution of certain internal organs). The principal stimulus for appendage
regeneration appears to be injury, nor does it seem to make much
difference what the nature of the trauma may be. Regenerative growth
has been observed as a result of ligation of limbs, the transplantation of
living or devitalized tissues under the skin, the subcutaneous implantation of carcinogenic substances, exposure to ultra-violet irradiation,
and deviation of nerves to wounded regions. It has been occasionally
claimed that some of these treatments act in specific ways to bring about
regeneration, but in view of the diversity of such successful methods it
would appear likely that nonspecific injury may be the stimulus common
to most. Whatever the method of induction, regeneration under these
circumstances results in the production of supernumerary outgrowths.
The kind of structure formed is entirely dependent upon its location and
characteristic of the appendage being replaced. This cellular differentiation proceeds in a remarkably orderly way, each tissue developing in
precisely the correct position in continuity with the corresponding tissue
in the stump. Concomitant with the proximo-distally directed differentiation, the entire structural pattern of the regenerate takes shape,
reflecting the operation of morphogenetic influences. The latter somehow direct the spatial organization of the competent tissues, are responsible for the general orientation of the regenerate and ensure the production of a whole, well-integrated appendage. The aforementioned
processes, to be considered below in greater detail, all occur in a temporally and spatially co-ordinated sequence culminating ultimately in
the cessation of growth once a complete regenerate has been produced.