Like most other affections of the osseous system, the causes that lead to the production of this disease are involved in the greatest obscurity. Unquestionably they sometimes appear as the results of accident, but then, when other and more severe injuries constantly occur without inducing such a consequence, the unavoidable conclusion must be that some peculiarity of constitution predisposing to the disease exists in the individuals who suffer from it. Exostosis has been seen, though not frequently, at a very early period of life; it has occurred idiopathically and attacked several bones in the same individual at the same time; after complete removal it has grown again with an inveterate pertinacity, and we have seen it in two or more individuals of the same family. Boyer4' considers the venereal poison to be the most common cause of exostosis, scrofula to have but little connexion with it, and scurvy still less. Other French writerst take a more extensive range, and adduce as causes, accident, cutaneous affections, scrofula, scurvy, cancer, and venereal. We cannot coincide with any of these opinions. Scrofula, when it attacks a bone, produces a destructive caries, and not an adventitious growth; scurvy, a softness or brittleness of bone. If there is any idiopathic disease of bone bearing the smallest resem blance to cancer, it is osteo-sarcoma, and vene real or even mercury we suspect to have a closer connexion with caries than exostosis.
In every form of exostosis, no matter from what cause proceeding, (and we have seen that its exciting causes are sufficiently obscure,) the surface of the bone and its substance to some depth become altered into a structure nearly resembling that of the morbid growth. Patho logists are not agreed as to whether this altera tion should be attributed in the first instance to an inflammatory process within the perios teum or the bone itself. Mr.Cramptont makes the terminations (as they are technically called) of chronic inflammation of the periosteum to consist in cartilaginous thickening of the mem brane, absorption of the subjacent bone, or the deposition of an undue quantity of bony matter upon its surface, the first and last of which are evidently forms of exostosis. How ever, leaving this part of the subject, which after all is not of much practical importance, still unsettled, it may be remarked that whether the morbid action commences in the bone or not, this latter structure is always extensively engaged. Exostosis is seldom to be met with like a circumscribed tumour in the soft parts connected by a narrow neck or bounded by a well-defined base; on the contrary, the bone forms a considerable portion of the swelling, which generally seems to spring gradually from an extended portion of its surface.
The symptoms of exostosis may be arranged into those produced hy the inflammatory or other diseased action within the bone or perios teum, and those occasioned by the pressure of the tumour on the adjacent organs. In general it is said not to be very painful nor very sen sitive to the touch, but this opinion must be received with great limitation. We have wit
nessed the case of a young gentleman who had exostosis on the front of both Here was neither nerve to be compressed nor muscle to be interfered with, yet the pain was so great that lie insisted on their removal. The part was as hard and firm as ivory, and removed by the mallet and chisel. His sufferings were extreme : he was subsequently attacked with erysipelas, and his life brought into extreme danger, yet did he not regret his pain and the risk he ran when considered as the price of the relief he had obtained. The pain in this case could not be regarded as the result of pressure on any very sensible structure.
However, the situation of the tumour may not only occasion a great aggravation of suffer ing, but be the cause of very formidable occur rences. We have seen a very small exostosis, not larger than half a marble, prove the apparently exciting cause of epilepsy, which for years embittered the patient's existence, and at length brought it to a termination. Indeed, it can scarcely be necessary to adduce instances in order to prove that morbid growths from the internal table of the skull may prove detrimen tal or even destructive in a variety of ways. Such g,rowths from the bottom of the orbit very generally destroy vision by protruding the eye from its socket; from the maxillee they may interfere with respiration or deglutition; and in any situation where there are muscles, they must more or less change their direction or otherwise impair their motions. But beyond this they cannot be considered as malignant— they do not involve adjacent structures in a disease similar to themselves, they do not ulcerate, neither do they contaminate the sys tem through the medium of the absorbents. The vascular organization of an exostosis seems to be inferior to that of the bone from which it springs, and to the healthy structures whether bone or cartilage that it may appear to resem ble; its growth is therefore in general slow and its size moderate ; but its increase is progressive, and there is no limit to the size it may ulti mately attain, in this respect differing from the node, which soon attains its proper dimensions and does not increase subsequently. The same deficiency of organization causes it to endure an attack of inflammation but badly, and therefore, when subjected to any irritation or even exposed to the influence of the atmos phere by the ulceration of the superincumbent tissues, it is prone to fall into mortification, which is one of the methods by which a natural cure may be accomplished. Not very long since a man was operated on in the Meath Hospital for the removal of an ivory-like exos tosis from the tibia, but the tumour was so hard as to resist chisel and mallet and every instrument that could be employed, and, filially, the operation was abandoned ; yet was the case ultimately successful, for the exposed tumour sloughed, exfoliated, and the patient left the hospital perfectly well.