Soon after the secretion of pus is established granulations are developed, and a state favour able to adhesion is produced. The develop ment of granulations occurs in the following manner :—upon the surface, about to suppurate, is exuded a layer of " coagulable lymph ;" this lymph becomes penetrated by bloodvessels, nerves, and absorbents, which give birth to granulations. These granulations are developed much earlier in some tissues than in others— in a stump, for instance, we see them first upon the cellular tissue, then upon the mus cular, then the fibrous, and lastly upon the osseous tissue : they appear to form as much more readily as the tissue may be more cellular and vascular. That these organs are very vas cular is evident from the rapidity with which they bleed upon the slightest contact ; that they contain nerves is shewn by the pain which is produced in them by the slighest touch : does not their prompt destruction by slight causes seem to indicate the existence of absor bents ? No one has made more interesting researches into the nature of these bodies than Sir Everard Home." He carefully observed the changes which occurred in an ulcer of the leg. By using a lens which enlarged objects eight times, he saw that granulations were formed in the fol lowing manner : first, is seen a mass of capil lary vessels differently arranged ; secondly, small sinuosities containing pus. The ulcer ob served during ten minutes, offered, in the first place, an extremely thin and transparent pel licle, under which were disengaged globules of gas, then canals having a horizontal direction, and containing blood. The tunics of these vessels were so delicate that they were ruptured by the simple motion of the leg. These canals anastomose with each other, taking different directions ; those which are developed the first were the next day changed into true vessels. Soon these new vessels have enough of solidity to admit of our passing a needle under them and raising without rupturing them. The forma tion of all these parts is due, according to Home, to the coagulation of pus, and the de velopment of carbonic acid gas ; " for if the puriforrn matter be wiped off, these phenomena are not produced." When, on the contrary, he employed substances, calculated to coagulate the pus, the formation of those vessels accelerated. He concludes from his experiments that bloodvessels are developed, almost as it were under the eye of the observer ; that they are not a prolongation of pre-existing vessels ; that they are formed independently of the action of the subjacent solid parts. So far, therefore, although the processes may differ, yet the general points of union between the two modes is singularly similar.
While suppuration is proceeding, another operation is in progress under the layer of gra nulations. A stratum of cellular tissue, at first simple and not very resistent, afterwards fibro cellular, and lastly fibrous, is organised insensi bly to serve as the base of the succeeding me dium of union.
When granular surfaces are brought into con tact, and the tendency to secrete pus has ceased, they enter into adhesion. This tendency is marked by a diminution of activity in the gra nulations; the membrane ceases to secrete pus, and the granulations become firmer and con tracted : before union can be effected, the sup purating surface must, therefore, change its nature—must be destroyed. A state like that in simple union by the first intention is produced ; the secretion becomes plastic, and somewhat analogous to that which accompanies that mode of union. •
When these new tissues or media of union are developed between surfaces naturally free, the structure of the two portions of the organ between which they are seated becomes changed. In serous or mucous membranes, as well as in those surfaces which are immediate modifica tions of these two systems, this may be ob served. When, for example, the pleura costalis becomes adherent to the pleura pulmonalis, the point of union is no longer a serous membrane; the free surface having disappeared, an un interrupted continuity is established between the subserous cellular tissue of the pleura cos tabs, and the interlobular cellular tissue of the lung. This conversion is frequent in the peri toneum ; in the tunica vaginalis a similar effect is produced by the common operation for by drocele ; in synovial membranes a similar effect occurs in what is termed false ankylosis.
Having described the general laws by which the phenomena of adhesion are governed, I shall now point out, generally, the modifica tions which are impressed upon it in different tissues.
It is upon serous membranes that we may with most advantage study the process of ad hesion, not only because it is more rapidly developed there, but because it much more frequently occurs there than in other tissues. If we examine the surfaces of two such mem branes which have been recently united, com mencing at a certain distance from the point of adhesion, we see the layer of coagulable matter effused between the two surfaces become thinner as we approach the point of contact. If the adhesion be sufficiently recent to admit of our separating the surfaces, we see the intermediate layer tearing, but remaining adherent to the inflamed surfaces. If the inflammation be more advanced, and the pseudo-membrane be more dense and organised, we find that the very thin layer of new deposition by which the union has place is more resistent than the thicker layer of organisable matter by which it is surrounded ; and at a later period we may discover vascular filaments attaching the ad herent portion of the new tissue to that, upon which it has been developed. These filaments are as much more evident as the adhesion is more immediate : of this we may very easily assure ourselves by cutting transversely two portions of digestive tube which have become to a certain extent adherent by their external tunic. The adhesion may be already very solid at the points where contact is so imme diate that we can scarcely distinguish the in terposed matter. Very delicate red capillaries creep through this matter, whilst perhaps at the distance of some lines, and even at the centre of an already organised point, the contact having been less immediate, a plastic layer of one, two, or more lines in thickness, may be seen uniting the surfaces, but not presenting either the solidity or the organisation of the exces sively thin layer which adjoins it.
When these adhesions have existed for a cer tain time, the serous structure completely dis appears. This destruction of serous membranes at the adherent point is very evident around herniae which have been inflamed ; the intestines engaged in the tumour are enveloped by a more or less dense layer of cellular tissue ; and hence many hernim thus circumstanced have been described as having no hernial sac. This sac has, however, originally existed, but has disappeared by the adhesions which have been formed between it and the displaced organs, adhesions by which the cellular tissue which replaces the serous membrane has been deve loped.