PRODUCTS, ADVENTITIOUS. 



139 



co-existing with all varieties of textural 

 change, and exercising important influences 

 on local nutrition, induration-matter would 

 require a volume for its full description. We 

 must content ourselves with an enumeration 

 of some of the principal sites in which it 

 occurs. Induration-matter forms: (A.) On 

 membranous surfaces, where it is known under 

 the names of pseudo-membrane, matter of 

 adhesions, &c. Of the serous class the pleura 

 is by far its most common seat ; next follows 

 the pericardium ; then the peritonaeum ; then 

 appear the tunica vaginalis and sy no vial mem- 

 branes ; and longo intervallo the arachnoid.* 

 Among mucous membranes it appears on the 

 respiration- surface in croup, plastic bronch- 

 itis, and pneumonia (in all which situations 

 it is not distantly allied to diphtheritic de- 

 posit), and on the intestinal surface as in 

 dysentery. It appears on the endocardial 

 and valvular surfaces in the warty and gra- 

 nular forms ; in the arteries and veins in the 

 patch-like shape. The so-called glands of 

 Pacchioni illustrate its occurrence on fibrous 

 surfaces (B.) Free in cavities. So it has 

 been occasionally found forming rounded 

 masses in the peritonaeal and pleural sacs ; the 

 so-called " loose cartilages" in joints are in 

 the great majority of instances composed of 

 induration-matter; so too are those small 

 melon-seed-like bodies, producing double 

 saccular distension at the wrist-joint.f (C.) 

 In the cellular membrane. The sub-cutaneous, 

 (less frequently than the sub-mucous, and still 

 less than the sub-serous) cellular membrane, 

 becomes infiltrated with this material ; in 

 parenchymatous cellular tissue it is singularly 

 common. In addition to the ordinary cases of 

 its occurrence in the latter, as a result of simple 

 inflammation, it constitutes in great part the 

 substance of the morbid element infiltrating 

 the kidney in certain cases of renal disease 

 attended with persistent albuminuria, urine of 

 low specific gravity, anasarca, &c.; infiltrating 

 the capsule of Glisson, it plays a notable (but 

 not the whole) part in hepatic cirrhosis ; 

 and infiltrating the substance of the lung 

 (especially in certain cases of empyema), it 

 converts that organ more or less completely 

 into a chondroid mass. Seated in the intra- 

 serous fibro-cellular tissue of the cardiac valves 

 and chorda? tendinese (where it is associated 

 sometimes with atheroma) its contractile force 

 produces the puckerings and shortenings so 

 frequently observed. (D.) As imperfect cica- 

 trix. Wherever a solution of continuity oc^ 

 curs, the cicatrix may be formed of this sub* 

 stance >, take the instance of false joints: in 

 some situations cicatrix seems always to be 

 thus constituted, of which more in the next 

 section. (E.) On new surfaces. Induration" 

 matter may form on wounded, burned, 



* We have never seen arachnoid adhesions, un- 

 less in connection with tumour of the brain or 

 menihges. Is idiopathic arachnitis always fatal ? 



f We have found these bodies hollow centrally ; 

 their capsule is composed of amorphous albuminous 

 matter with a little fat, and occasionally calcareous 

 particles. 



and ulcerated surfaces; and supply a sac 

 more or less perfect round the cavity caused 

 by abscess, tuberculous softening, and fibulae. 



SUB-ORDER II. 

 SIMULATING THE NATURAL TISSUES. 



When endowed with higher plastic quality 

 exudation does not remain as induration-mat- 

 ter, but becomes the matrix from which a 

 structure more or less closely imitative of 

 some natural tissue is evolved. This imita- 

 tion is never perfect, at once physically, 

 chemically, and physiologically, at least in 

 respect of the higher orders of texture. A 

 pseudo-tissue thus generated may be wholly 

 adventitious ; or partially so, as when design- 

 ed for the reparation of lost parts. 



EXTRA-VASCULAR TISSUES. 



Epithelium. On cicatrising and on fistulous 

 surfaces, on the inner wall, or amid the con- 

 tents, of cysts, as a coating for haematomata, 

 and as a lining for new vessels, tessellated 

 epithelium occurs as a purely adventitious 

 product. The retained and accumulating 

 epidermis forming corns and callosities, or 

 that thrown off in excess from the skin in pi- 

 tiriasis, or from the genito-urinary mucous 

 surface in various states of disease, or from the 

 intestinal surface in cholera, &c., can only be 

 viewed as products of supersecretion. Hy- 

 pertrophy of the papillae of the skin, with 

 excess of epidermal formation (Univ. Coll. 

 Mus.), a state prone to give rise to obstinate 

 ulceration, cannot fairly be considered under 

 the present head. Perhaps the epithelium 

 accumulated in cutaneous sacs procluced by 

 dilatation and occlusion of sebaceous follicles 

 may be considered adventitious. So likewise 

 are those productions, elongated or flat, known 

 as " horns," and which are essentially com- 

 posed of epidermis. Commonly springing 

 from a dilated and diseased sebaceous follicle, 

 and mixed abundantly with fat, slightly with 

 saline matter, the basis of the future "horn" is 

 at first soft, subsequently becomes inspissated 

 and hard, when its increasing dimensions, 

 carrying it beyond the limits of the follicle, 

 place it under the influence of the atmosphere. 

 Layer upon layer of epidermis continues to 

 accumulate at the surface of the follicle, and 

 eventually a conical mass, some inches in 

 length, may be the result. Horny-looking 

 productions sometimes form on ulcerated 

 surfaces, simple or cancerous. 



Pseudo-tumours, composed essentially of 

 epithelium, and susceptible of vascularization, 

 form, it is affirmed, on some mucous surfaces, 

 ^the uterine for instance. We have not 

 met with productions of this kind. 



Nail. (See TOOTH, p. 143.) 



Cartilage.-*- Adventitious cartilage, at one 

 time believed to take rank among the most 

 common, is now known to be one of the 

 rarest of new formations : the microscope 

 has certainly dispelled a cloud of error on 

 this subject, by simply showing that cartilagi- 

 nous-looking products are not necessarily 



