1. It occupies, as we have stated, a smaller space, having by its contraction drawn the surrounding skin inwards, and thus, by the wise economy of nature, diminished the surface requiring new skin to cover it. This is of course most strikingly seen in those parts where the cellular texture is loose and yielding, as in the scrotum, where a large loss of skin is often healed with only a very small cicatrix. On the contrary, parts that cannot so yield are healed with a proportionately large cicatrix, as in wounds of the scalp, &c. 2. The texture of the cicatrix is frequently harder and thicker than the natural skin. This circumstance varies considerably, but we believe this variation will be found to bear a pretty exact relation to the degree of contraction, to the length of time occupied in the cure, and to the irritation to which the ulcer was subjected in the process of healing. When these have been considerable, the hardness is correspondingly great, while, if the cure has been expeditious and the part been kept extended and irritation avoided, the cicatrix remains soft, thin, and pliable, a point of great importance in practice as applied to the healing of burns. 3. The colour of the new skin is different from the natural parts. This arises from the want of rete mucosum,. which is not regenerated till long after the other tissues, and sometimes not at all. For this reason a cicatrix in a Black is as white as that in an European ; but after a considerable lapse of time, this structure is sometimes formed anew, and in some instances becomes even of a darker colour than before. 4. The surface is perfectly dry from the want of ex halent pores, which are never found to be restored even in the oldest cicatrices. Indeed, in cases where the chorion ha.s not been de stroyed through its entire thickness, the loss of substance reaching only through its outer layers, these pores are generally obliterated, and the important exhalent function of the skin is annihilated ; and even when the injury has extended only through the external vas cular structure of the skin, as is the case in the healing of a blister vvhich has been long in flamed, we have observed a drier state of the parts, and more polished than the surrounding skin which had not been injured. From this pe culiarity in the cicatrix, when the whole body is bathed in sweat these parts are dry and po lished. This state of dryness, however, partly results from another anatomical deficiency, namely, of the perspiratory glands, which are destroyed in cases where the entire integument has been injured, and these are of course never regenerated. 5. The new tissue contains no hairs, and if, after superficial wounds, a few scattered hairs appear on the surface, they are feeble and white. 6. After the healing of a large ulcer of long stanCiing, the new surface is sometimes much lower than the surround ing skin. Nature seems, in these cases, to have exhausted her energies in the long en deavour to heal the ulcer, and the granulations never rise to the level of the surrounding skin, as in recent cases. The new cuticle there fore commences upon those granulations which shoot from the elevated edges of the ulcer, and the cicatrizing process is thus led as it were into the hollow of the ulcer, and spreads along its surface, completing the cicatrix in an exca vated form. 7. The elasticity of the cellular tissue under the new chorion is less than that of the ordinary cellular web; nor does it allow of distension to the same degree. This is seen in cedema and emphysema, where this part will often remain depressed while the sur rounding parts are raised and distended ; it is also seen in the impediments which large cica trices prove to the movements of the joints. The same circumstance perhaps also gives a reason for there being no fat contained in these parts. This want of extensibility seems to be but one consequence of the law which reou lates the products of inflammatory action. The elastic power is materially diminished in the natural cellular tissue by inflammation, a de gree of stiffness and difficulty of movement remaining for a long time after ; and as the tissue of a cicatrix is, ab initio. the product of inflammatory action, it is to be expected that it should shew the same effects.
How far are the vascular and nervous func tions of the lost part restored in the cicatrix ? It is probable that the new structure receives nerves, but in small number. Of those senses
which can be implicated in the destructive process of ulceration, that of touch alone seems to be restored. This is so in a marked though still imperfect ,clegree; the sensation in these parts being somewhat of that dull kind expe rienced after paralysis.
On the temperature of the cicatrix we have not made sufficient observations to generalize, but we have found that the actual temperature of the bridle from a burn, while it retains its hardness, is several degrees above that of the healthy skin, while the power of retaining its temperature, or Of resisting the extremes of heat and cold, is much inferior in the cicatrix to that which the healthy skin possesses, although the actual temperature, under ordinary circum stances, is the same as the surrounding skin. Almost every traveller to the Poles or to the Tropics mentions the liability of old'ulcers that had been healed, to announce the extremes of temperature by pain and inflammation. .
The bloodvessels of the new structure are at first numerous, as indicated by the redness and the readiness with which it bleeds, but after wards they diminish much in size and number, so that, in an old cicatrix, it is often impos sible to force an injection into them. M. Du puytren tells us that in scars upon the face the greatest heat from exercise, or the influence of the mind in producing blushing, leaves this part uncoloured amid the surrounding redness.* Bichat assures us that even the new epidermis itself is overrun with bloodvessels.f We have certainly never been able to discover the least trace of vascularity in it, nor have we found that sensibility in this part which he describes. It seems to be a matter of doubt at present how far the function of secretion exists in the new production. Dr. Bright seems to believe in its restoration, since he says that the scar in one of his observations appeared to be covered with a true mucous membrane ; but it is right to state that the proof he gives of this is rather equi vocal, namely, that the' surface was quite con tinuous with the membrane lining the rest of the canal; " indeed," he adds;." when inspect ing the ulcer in the process of healing, we per ceive the vessels of the mucous membrane running over the surface to be repaired."T M. Troillet mentions in round terms that the ciCa trix had the thickness, consistence, and al:4.: pearance of mucous membrane ;§ but neither he nor Dr. Bright says any thing in particular as to the villous structure, which we conceive to be an essential characteristic of some forms of mucous membranes.* Dr. Hope's and NI. Bil lard's cases were destitute of' villi, and the latter expresses a doubt whether it ever takes place. Our own observations decidedly incline us to the same opinion.
Like all adventitious organic products, cica trices are very readily irritated and are de stroyed by ulcemtion with amazing rapidity. A few days and even a few hours are sometimes sufficient to undo the restorative labours of many months; but tbis destruction is often su perficial, and then the after-healing is as rapid as the previous ulceration.
M. Dupuytrent informs us that the cicatrix resulting from an entire destruction of the skin is not liable to be affected by many exanthe matous diseases, such as scarlet fever, measles, and small-pox; it remains pale in the midst of the inflammation and eruption which covers the neighbouring parts. The contrary takes place only in superficial cicatrices, under which some layers of the original cutis exist, and which participate in the properties as well as in the inflammatory tendencies of the rest of the skin.
In conclusion we may state, that it appears, from the previous considerations, that in the repairina of the injuries in question beautiful as is the process and useful as are the results, yet nature's great object does not consist so much in an endeavour to restore the lost struc ture in all its functions and perfections of organization, as merely to produce a covering for those parts which remain uninjured, to act as a defence to them from external irritations and injuries, and possessed therefore only of such a degree of vitality and of such properties of structure as shall be sufficient for its own preservation and repair.
(A. T. S. Dodd.)