CYST. 



789 



being almost constantly lined by an inorganic 

 coat, which is sometimes susceptible of being 

 divided into laminae ; when this coat is re- 

 moved, there remains a very thin cellular mem- 

 brane. If the lining membrane be irritated, 

 the secretion as well as the membrane may be 

 modified ; and the variety of these subcuta- 

 neous tumours is thus explained. 



Other cysts differently formed appear to ar- 

 rangfe themselves most naturally in this class ; 

 of such are those which succeed to the ob- 

 struction of a salivary duct, ranula for instance ; 

 those which succeed to a fistulous canal, and 

 are produced by the obliteration of the orifices 

 of such canal ; the mucous tissue by which 

 the canal was previously invested becomes 

 changed in its organization, and a serous cha- 

 racter is acquired : those which are occasionally 

 produced in the lungs, by the obliteration of 

 the canal of communication between a tuber- 

 cular cavity and a bronchus ; in this case 

 also a serous membrane is developed within 

 the cavity. 



The second class. Every foreign body, fluid 

 or solid, formed within or derived from with- 

 out the animal economy, induces in that eco- 

 nomy an effort at expulsion. Whether the 

 body be a shot, a bullet, or other projectile, or 

 whether it be extravasated blood, stone in the 

 bladder, the foetus in extra-uterine pregnancy, 

 acephalocysts, tubercle, or other heterologous 

 or analogous formation ; in all cases irritation 

 or inflammation is developed, for the purpose 

 of expelling or isolating the nocuous body. 

 If it be in its nature irritating, it excites in- 

 flammation, and is expelled with the pus which 

 has been secreted around it; if it have no 

 mechanically or chemically irritating property, 

 it may remain in the midst of the organ, some- 

 times passing from cell to cell, obedient al- 

 ways to a kind of eccentric movement ; some- 

 times nature isolates it by organising around it 

 a cyst which is adherent by its external surface 

 to the surrounding tissues, but which is free 

 and smooth internally, furnishing a fluid by 

 which many of these bodies may be broken 

 down, and as soon as they are removed, the 

 walls of the cyst become reduced into cellular 

 tissue by absorption. 



Frequent opportunities are afforded for ex- 

 amining these structures in the cellular tissue. 

 When a certain quantity of a succulent fluid is 

 accumulated in this structure, if it cease to 

 increase, the parietes of the cavity which con- 

 tains it continues to be the seat of a chronic 

 inflammation by which the formation of a cyst 

 is determined. Until the organisation of this 

 cyst is perfected, the surrounding cellular tissue 

 continues red and indurated; but as soon as 

 the organ is completed, this redness and in- 

 duration are commonly in progress of dis- 

 sipation ; in some cases, however, they remain, 

 and then it occasionally happens that the cyst 

 participates in the morbid action, and the in- 

 terior of the cyst may have a pseudo-membrane 

 developed on its surface. Cysts so developed 

 are at their commencement soft, not very con- 

 sistent, and may be easily detached from the 

 surrounding structure. The inflamed stratum, 

 between the cyst and the adjacent healthy 



tissue, gradually acquires a greater density and 

 more power of resistance, ;tt the same time 

 that it becomes thinner, and contracts a more 

 intimate union with the proper membrane of 

 the cyst. When the organisation of this spe- 

 cies of cyst is completed, the membrane is 

 whitish, opaque, more or less thick, and as a 

 point of comparison, denser, and thicker th;m 

 a serous membrane, and it presents a surface 

 somewhat similar to that membrane. 



In making a third class, it must be obvious 

 that we incline to the opinion of Delpech, 

 " that certain cysts do not proceed from an 

 accidental and mechanical modification of the 

 cellular tissue," but that they are so many new 

 organs, so many newly developed tissues, 

 which do not possess either the same degree or 

 even the same kind of vitality as the surround- 

 ing parts. 



In this class we range those which contain 

 a serous or sero-mucous fluid, which are de- 

 veloped in various parts of the body. Their 

 parietes are sometimes transparent, at others 

 opaque ; upon their inner surface they usually 

 present a kind of tomentum or velvet-like tex- 

 ture, sometimes it presents hair. Their ex- 

 ternal surface is sometimes free on all sides 

 except that upon which the vascular commu- 

 nication obtains, sometimes they are com- 

 pletely adherent. They are observed free and 

 almost floating in the cerebral cavities, in the 

 kidney, the liver, the lungs, and in all serous 

 cavities. 



We also include in this class certain syno- 

 vial cysts, which are observed around the 

 articulations of the hand, of the foot, some- 

 times of the knee, and in the neighbourhood 

 of the sheaths of tendons. Some persons have 

 been disposed to refer the origin of these 

 organs to a displacement of the synovial mem- 

 brane which has yielded at this point; but ob- 

 servation has demonstrated that they are cysts 

 with dense and fibrous external, and serous 

 internal parietes, developed in the cellular 

 tissue surrounding the normal synovial sac. 



In the same class we place a species of cyst 

 developed, so far as we yet know, under the 

 anterior annular ligament of the carpal articu- 

 lation, more rarely in the vicinity of the 

 tibio-tarsal articulation, but always around sy- 

 novial sacs or tendons, and essentially con- 

 stituted of small white bodies, in appearance 

 similar to small grains of boiled rice. 



Of the serous cysts, we may frequently find 

 some very small, and, as nearly as may be, 

 empty, the membrane being puckered and 

 plicated, and in contact with itself at points 

 where the plicae meet. At a certain period of 

 their existence there is scarcely a particle of 

 fluid accumulated in them, and of course the 

 first exaggerated exhalation which has place 

 will be lodged without any obstacle in the 

 cavity, the plicae will be effaced, and the pa- 

 rietes removed to a certain distance, the one 

 from the other. It is probable that this pro- 

 portion between the cyst and its contents is 

 maintained until some irritation shall acce- 

 lerate the exhalation, much as in the serous 

 cavities of the body. This exhalation is some- 

 times so abundant and rapid that the parietes 



