Page:The American Cyclopædia (1879) Volume VII.djvu/40

 EXOSTOSIS EXPANSION all other tissues of the system, takes on a mor- bid development, an eccentric hypertrophy of its substance, forming a well denned tumor on its surface by the mere excess of interstitial osseous deposit ; in the other the new ossific matter is deposited originally on the surface, under or between the laminae of the periosteum, separated from the bone at first by cartilage, but afterward becoming consolidated to it in the usual manner of bony processes. The first variety may affect the greater part of a bone, and deserves rather the name of hyperostosis ; and the second, by the process of ossification, may be converted into the first ; this distinc- tion is of considerable importance in the prog- nosis and treatment of the affection. The muscles and soft parts over an exostosis are generally not changed, unless the tumor be of considerable size and in the neighborhood of large nerves and vessels ; but the periosteum is almost always thickened, and less adherent to the bone than usual. In the first variety the form is regular, and the bony fibres diverge from the natural direction to enter the tumor, as in other forms of eccentric hypertrophy ; in the second variety the form is irregular, of- ten fantastic and rough, and there is an evi- dent base by which it is as it were immovably articulated to the supporting bone, except in very old growths; this base in recent cases is cartilaginous and readily separated, and shows that this kind of exostosis originates from and is nourished by the investing periosteum; it indicates also a method of treatment which has been found successful, by denuding them of their periosteum and causing their necrosis and separation from want of nutrition. If the cartilaginous base rests upon the bone, un- der the periosteum, the removal of this mem- brane will cause an exfoliation of the subjacent bone ; but if between the laminae of this enve- lope, a similar operation will effect the fall of the tumor without injury to the surface of the bone ; the cartilage soon becomes ossified, and the exostosis forms one body with the bone, resembling the first variety in having no basal line of separation. In course of time the ex- cessive deposit of phosphate of lime in these growths may convert them into a substance having the appearance, consistence, weight, and polish of ivory. Among the constitutional causes of exostosis are syphilitic poisoning, the scrofulous diathesis, and the gouty and rheu- matic conditions; the immediate cause is in- flammation, produced by mechanical or other means, leading to a deposit first of plastic and then of osseous matter, the development being similar to that of normal bone. In some con- stitutions there is such a disposition to the de- posit of ossific matter, that the slightest con- tusion is sufficient to cause the development of these bony growths, not only on bones but in the substance of tendons and ligaments ; and the affection is often hereditary. When the growth takes place in the cavity of a bone, as in the cranial cavity, it has been called en- ostosis, but with doubtful propriety, because in this case the growth is upon the bone and out- side of its structure. The prognosis varies, principally in proportion to the rapidity of the growth, which when very slow may not be much regarded, except when interfering with the functions of some important organ, as a joint, or into the cranial cavity. The treat- ment also varies with the prognosis. Often the removal is not a matter of moment, as ex- ostoses may be carried through life without much inconvenience ; and the removal may be a hazardous undertaking, as when the tumor encroaches upon a joint whose cavity would become opened by the operation. If the cir- culation in an important artery is impeded, re : moval becomes desirable, and should be under- taken when there is reasonable hope of a suc- cessful result. Topical applications are often beneficial, and in the earlier stages, in the form of blisters and strong counter-irritants, often effect the removal by absorption. A strong tincture of iodine, or a solution of iodine in iodide of potassium, is often very serviceable. The constitutional treatment, particularly when syphilis has preceded the affection, should not be neglected. Preparations of mercury may be cautiously administered, particularly the iodide, and iodine may be given in combination with potash or soda salts. When much pain is experienced, anodynes may be administered, either by the mouth or topically. EXPANSION, the property displayed by mat- ter of enlarging in bulk by diminution of pres- sure, increase of heat, or in a few instances by increase of cold, and also of moisture. It is seen in solids in the common operation of set- ting the tire of a wheel ; the iron ring, being heated in the circle of burning chips and coals, enlarges in bulk so as easily to slip over the fel- ly, which it compresses tightly as it grows cool on the application of cold water. It is seen in liquids in the rise of mercury in the thermome- ter ; and in aeriform bodies in the ascending cur- rents of heated air, or more plainly in the burst- ing of a tight bladder as the air it encloses swells by exposure to heat. The amount of expansion exhibited by different bodies by any given increase of heat is very various. Those only which exist in the aeriform state, or as vapors, can be classed together in this respect. They all expand very nearly if not exactly alike by the same increase of temperature. Like air they increase in bulk from the freezing to the boiling point, so that, according to Gay-Lus- sac, 100 measures at the lower degree fill 137i at the higher. For each degree of Fahrenheit the expansion of air, according to the accurate determinations of Eegnault, is, under a con- stant volume, ^-^ of its volume ; for the less condensable gases it is perceptibly larger. Each solid body has its own rate of expansion, which however is not uniform for equal incre- ments of temperature, but increases at high degrees in a faster ratio. This, unless special allowance is made for it in the graduation, in-