366 PATHOLOGY wanting in red blood-disks, and with the colourless corpuscles in enormously disproportionate numbers. We shall afterwards see that there is a kind of blood leucocythremic blood which ap proximates to pus in these its essential characters. That which distinguishes the process of repair from the forma tive process in the two cysts, and in all tumours whatsoever, is that the former is self-limited ; after a time skin forms on the surface of the granulations, and the lower layers of cells pass into the resting condition of fibrous tissue. Each of these adaptations has now to be described. Skin-for- Formation of Skin on a Granulating Surface. The new skin mation. appears as a delicate bluish frill extending gradually over the raw surface from the margin of the old skin. Nothing is more natural, therefore, than to suppose that it is a continuous growth from the cells of the rete mucosum of the old skin ; and, according to the embryological dogma of an impassable gulf between the epiblast, mesoblast, and hypoblast for histogenetic purposes, the new epidermis can have no other source than proliferation from corre sponding cells of the old. But, dogma apart, there is a radical difference of opinion as to the origin of the epidermic or epithelial cells on the surface of granulations. Notwithstanding the fact that the new epithelium springs up alongside the old, it has appeared to many observers with the microscope that it was derived, not from subdivision of the latter, but from the granulation - cells becoming flat and otherwise adapted to surface purposes. In considering these difficulties let us, as before, seek analogies among other formative incidents of mature life. In the first place it should be mentioned that the new skin may be peculiar. The accompanying figure (fig. 11) is drawn from a section through the Giant- cells. FIG. 11. Loop-like arrangement of rete mucosum in the skin of a scar. scar of an ulcer of the leg which had broken out and healed re peatedly. The peculiarity is that the epithelial cells are every where a narrow belt which bends down and encloses the terminal vessels as in a loop ; in other words, the surface vessels are driven through the midst of the rete mucosum of the new skin. For an analogy to this epitheliation of granulation-tissue we may take the case of the cyst already referred to ; it was covered in part with a thick layer of epidermic scales. The origin of these in the cyst is not difficult to trace ; they are the **-_ granulation-cells enlarged, with two, " three, or four nuclei, and with a more homogeneous protoplasm. The surface-layer is in fact largely made up of multinuclear blocks, some of which become excavated in their in terior, while their nucleated peri phery forms a narrow belt of surface- cells with a descending loop enclos ing a space, in which collections of blood-corpuscles may sometimes be seen (fig. 12). If we imagine the plexus of vessels ramifying on the Flo . 12. From surface of a cyst granulating surface to form com- lined with epidermis ; above, a munications with these excavations continuous piece of the cyst- wall; ,, . , ill below, individual multinuclear in the multinuclear blocks, we ce jj s excavated, should be able to understand how it is that they are driven through the rete mucosum of a scar, as in fig. 11. Giant -cells in Repair. These multinuclear blocks are the so- called giant-cells. Their occurrence in fungous granulations was de scribed by Billroth (op. cit., p. 32) in 1856, he having previously seen them in the granulations of bone and taken them to be elements "necessary for the new formation of vessels in osteophytes or in cal lus. " The accompanying figure (Tig. 13) shows several examples of them from the granulations of a slow-healing sturnp. Precisely the same forms occur in the wall of the cyst whose structure has been already referred to in order to illus- Fia trate the granulations of repair. But for these multinuclear blocks of tissue we have a clear physio logical parallel in that unfailing source of analogies for the formative processes of mature life, namely, the placenta. The accompanying examples (fig. 14) are drawn from the deepest layer of a discoid placenta (the guinea-pig s). Here it is evident that they result from the subdivision of a single nucleus within single nucleus within a /^3 K*SStfl^ & K ^-> r< growing cell of the inner ( @$ A W/^&ft}^. $ muscular coat; and their (*?,-^- J ( -ii^ R ^^ i fi ("TT^rXxC place in the placental pro- ^V%/ . 3^ y^ P; ^ ^ " I -A j}-V r5V -f cess is as clear as their s)^ v ; ^ v Vv^/A^. - J^4r>Ttfv^& histogenesis. They enter {"?& - v_. r :> fo^- (C* into the formation of the blood-sinuses of the deeper parts of the organ, some times forming a consider able part of the wall of a vessel by being excavated in their interior (the nuclei being driven to the side), at other times forming one side of a blood-channel, a corresponding multiline- 1-pir block formin<r j-] 1(1 FIG. 14. ^ aso-formative giant-cells from deeper real block loiming the layers of placenta (guinea-pig), other, and the lumen of the vessel being the space between them. They represent a some what feebler continuation of those vaso-formative processes in the placenta which we have already used as the analogy for the pro duction of the new vessels of granulations. That their function and significance in granulations is not wholly vaso-formative will appear from the fact of their co-operating to build up the surface epithelium. Conversion of Granulation - tissue into Scar-tissue. The skin Scar - of a scar is never perfect ; it is always thin, wanting the descend- tissue, ing processes and papillae of the natural skin, and wanting also the hair -follicles, hairs, sebaceous glands, and sweat-glands. Its blood-vessels never become the orderly capillary loops of the original type ; they remain for a time as an extensive plexus of large vessels close to the surface, giving a recent scar its livid ap pearance ; afterwards the channels of the vessels become narrower, and many of them quite occluded ; and the scar has in the end a somewhat blanched appearance, which continues even when the surrounding skin is thrown into a state of ruddy glow. The underlying tissue, however, gradually acquires more of the natural type. If a section be made through an old scar it will be seen that the subcutaneous tissue is fibrillar and fibrous, with more or less of fat -cells. In the figure (fig. 15), drawn from a section FIG. 15. Scar-tissue of an ulcer of the leg which had broken out and healed repeatedly ; spindle-cells with brown pigment in the interfibrillar spaces. through the scar of an ulcer of the leg which had broken out and healed more than once, the tissue is composed of parallel wavy fibres, with spindle - cells between them at regular intervals, the cells having (as a characteristic of scar-tissue after repeated heal ing) brown pigment -grains in their substance. The successive changes which have led up to this horizontal fibrillation are not difficult to follow. While the ascending vessels acquire more and more of elongated cells on their walls, the granulation-cells in the intervals between them become extended horizontally or obliquely (see fig. 7), the spindle -cells among the fibrillar bundles in the figure being the surviving representatives of them. The change of the spherical cells into spindle-cells, which precedes the fibrillation, takes place first in the deepest or oldest stratum of the granula tion-tissue, and it appears to be accompanied by a certain dragging down or obliquity of the vessels running to the surface. There is always a considerable thickness of spindle -cells parallel to the vessels, so that these, together with the horizontal tracts between the vessels, make up a kind of warp and woof. But as the scar- tissue matures the horizontal bands come to overshadow the vertical or oblique. The fibrillation takes place, as it does in ordinary growth, in an intercellular or perinuclear homogeneous protoplasm, which becomes more extensive as the embryonic or purely cellular character of the granulation-tissue fades. One of the most striking facts in this development of embryonic tissue into mature tissue in the adult is its shrinkage, corresponding to the well-known con traction of the area of a healing surface. Repair of a Broken Bone. The reparative process in bone is Bone- much simpler and it may be said to be much easier than in the repair, healing of a stump. The bones retain even to old age the materials out of which new bone may be produced ; these are the somewhat
