.Adhesion.* Formation of callus.—The phe nomena attendant on this process are most easily and familiarly observed in the re-union of fractures. It is very remarkable, however, that considering the number of celebrated men who have directed their attention to this subject, and the opportunities for observation that are so constantly occurring, nothing has yet been positively determined. We have theories in abundance, apparently founded on and sup ported by experiment, but still so contradictory that it is impossible not to entertain a suspicion that the theories were in general formed in the first instance, and the facts, if they did not immediately apply, wrested a little in order to support them afterwards. Hence this part of our pathological studies consists of little more than a history of opinions and doctrines neces sary to be known as constituting part of the literature of the profession, but totally unavail able to any practical purpose.
The most ancient explanation of the process by which callus is formed is, that it wa.s per fected by means of a viscous fluid poured out, around and between the fragments of a divided bone, which were thus mechanically glued to gether. This fluid, which was termed the osse ous juice, was supposed to acquire the requi site consistence afterwards, and thus became the medium of a firm union. Nothing, how ever, was said of the time or manner in which the consolidation was effected, nor of the absorption of the superabundant part of this fluid subsequently.
The first who doubted this theory of the osseous juice, or rather who thought it insuffi cient, was_ Duhamel, a man of extraordinary ingenuity, but unfortunately not a physician, and therefore not qualified to examine or to explain the results of vital actions. He adopted his ideas as to the formation and growth of bone analogically from trees and vegetables, and supposing the periosteum to answer the same purpose to bone that the bark did to the wood, he conceived that ossification went for ward by the conversion of the internal layer of periosteum into bone. It was natural, having formed this theory as to the original conforma tion, to advance it still farther into an explana tion of the mode of re-union in fracture. He said that the extremities of the torn periosteum covering the fragments swelled ; that they met, and uniting, formed a kind of brace or ferule inside and outside of the fracture; sometimes, in case of the external membrane being torn off, the internal answered every purpose alone; sometimes the external periosteum was suffi cient, but in every case it was this that perfected the operation. It is needless now to canvass a theory that has long since been given up as untenable, yet as if to show how little of novelty can be expected in physiological rea soning:, it will be found that an opinion not very far removed from this in its bearings was the one entertained by Dupuytren, so recently lost to science.
The next opinion to be noticed is that of Haller. This great physiologist, who was a cotemporary of Duhamel,* quite dissatisfied with the ideas entertained in his time on this subject, endeavoured to develope the truth by experiments, and conducted many, in conjunc tion with a pupil of his named Dethlef. The result was, that the process of re-union ap peared to him to be the same as that of the original ossification ; 1st, that a gelatinous or gluey substance is poured out around the ends of the fragments ; 2d, that this substance be comes converted into genuine cartilage; and lastly, that an osseous deposit is laid down in the cartilage, forms a ring of bone, and gra dually increases until the entire ossification is completed. 'This theory is principally objec tionable in the regularity with which these changes are said to take place, whereas it is more than questionable vvhether this gelatinous fluid, the origin of the callus, ever becomes car tilage at all. Doubtless it is altered in con sistence and becomes hard and firm, opaque and elastic, and thus far resembles cartilage in its sensible qualities ;t but it is tinged of a red colour by feeding the animal with madder, which is not the case with cartilage; and che mical analysis shews its nature to be osseous and not cartilaginous. However, the experi
ments of Haller and Dethlef are entitled to great attention from the care with which they were conducted, and with a little modification their results are probably not very remote from truth.
Hunter, so happy in the doctrine of adhe sion, endeavoured to extend it as widely as possib!e, and has certainly simplified both our notions with respect to divided parts and our practice in procuring union, although his cor rectness in considering effused blood to be the medium of that union has been frequently doubted. According to him, the first effect of fracture is, the effusion of blood from the ruptured vessels of the bone and the adjacent structures : this blood becomes organised by vessels shooting into it ; whilst in the mean time the ends of the fragments inflame, and this inflammation produces adhesion in the surfaces that are even, and a disposition in the scales or points of the broken edges that re main, to be removed by absorption. Pretty nearly the same are the conclusions to which Mr. Howship arrived after a series of expe riments conducted with great accuracy and minuteness. This paper is in the ninth volume of the Medico-Chirurgical Transactions, in which these experiments (performed on the fractured bones of rabbits) are detailed and illustrated with engravings. They refer to the appearances observed on the third day, on the fifth, the ninth, the fifteenth, the twenty-third, and thirty-second days after the fracture. The relation of these experiments singly would occupy more space than can be appropriated to this part of the subject, and we must therefore confine ourselves to the conclusions as drawn from them by the author himself. He concludes that the first effect of fracture is extravasation of blood into the surrounding cellular struc tures, principally that of the periosteum ; into the medullary cavities of both fragments .and between their fractured extremities. This blood soon coagulates ; after some further time its colouring matter disappears ; and the thick ened periosteum becoming. more firm assumes the sensible characters of cartilage. The de position of osseous matter takes place within the coagulum, beginning at the part nearest the fracture and extending gradually from this point: it even commences in the clot situated within the medullary cavity before the colour ing matter is removed ; but under every cir cumstance and in every situation, we are to understand that the coagulum of blood is the nidus of ossification and the medium of union between the fragments. Notwithstanding the respect due to such high authority, there are many who do not believe in the possibility of effused blood becoming organised, and look with doubt and suspicion on every experiment and every observation by which such a doc trine is sought to be established. They reason, that if, under any circumstances, blood became the medium of union, we ought to leave the surface of a stump or other wound covered with clotted blood, and spare ourselves all the labour and pains we einploy in removing it and placing the cut surfaces cleanly in appo sition with each other. And they also remark that when a clot of blood is left behind, how very commonly, instead of becoming organised, it lies as a dead substance in the wound, im pedes the union, promotes suppuration, and imparts to the discharge a putrid and offensive odour. These pathologists suppose that in many instances the fibrine of the blood has been mistaken for coagulating lymph, which is the natural product of the vessels in the adhesive stage of inflammation, is capable of becoming organised, and ought to be the legi timate seat of any deposit to be afterwards laid down in completing the process of union.