SEROUS AND SYNOVIAL MEMBRANES. 



529 



adhesion of the cells, one might imagine that 

 the stratum ordinarily lasts a considerable 

 period without experiencing any desquamation 

 or substitution of new cells. And although 

 the ease with which a layer of cells is stripped 

 off by slight force might at first sight seem 

 opposed to such a notion of their durability, 

 yet it is tolerably certain that the mechanical 

 relations of the cells are so adjusted as to 

 allow the free gliding movements of their 

 moist, smooth surface with perfect impunity. 

 While, on the other hand, where the presence 

 of the tissue seems to fulfil its main object, a 

 mechanical one, and where the flattened epi- 

 thelium does not include the elements of a 

 secretion in any quantity, and consequently 

 would hardly fulfil any secretory purpose by 

 its occasional or exceptional separation ; to 

 what purpose should it be ever shed at all ? 

 The serous membrane exhibits one layer of 

 solid cells, all of which are related by one 

 (the nucleated) surface with the neighbouring 

 vascular supplies, while they present their op- 

 posite surface to receive a slight friction ; and 

 it does seem possible that the effete ma- 

 terials may be removed, the losses of friction 

 made up, and, in a word, the gradual exchange 

 which constitutes the nutrition of a tissue 

 accomplished, without the disruption of the 

 old cell and the substitution of an entire fresh 

 one. The cell-form does not necessarily 

 imply evanescence, and the centre of attraction 

 which it constitutes can hardly be supposed 

 unfitted for the processes of ordinary nutri- 

 tion, because it sometimes collects materials 

 which imply its destruction, or is thrust away 

 from the sources of nourishment by its fellow 

 vesicles. And if it should be asked, " Why is 

 the serous membrane constituted of cells, if 

 the ordinary form of nutrition would suffice?" 

 it might be pointed out that, although the 

 form of nutrition be the same, its pace may 

 and probably does attain a greater rapidity in 

 cells than in the more permanent textures, 

 and that by their instrumentality the rubbing 

 surfaces are everywhere separated by an ap- 

 preciable interval from the delicate capillaries, 

 a condition that could scarcely obtain in 

 areolar or ligamentous tissue, however it were 

 disposed ; and that in addition to this, cells 

 offer the mechanical advantage of forming a 

 smooth tesselated pavement, while they possess 

 the physiological merit of readily repairing the 

 accidents to which this tissue seems compa- 

 ratively more liable than others. 



The synovial membranes seem to differ from 

 the serous membranes in most of these 

 respects. The cells which cover the general 

 surface of the membrane are more spherical, 

 less uniform in size, and less accurately tes- 

 selated ; while on the highly vascular fringes, 

 the large, globular, and distended epithelia, 

 with their plentiful blastema, strengthen the 

 indications of .active secretion thus afforded. 

 The presence of synovia in considerable quan- 

 tity, and the recognition of the ordinary se- 

 cretory process, by the detection in it of relics 

 of ceils, chiefly nuclei, form another ground 

 of distinction. This secretion of viscid fluid 



VOL. IV. 



appears to be indirectly referrible to the greater 

 pressure exerted on these surfaces, and the 

 consequent necessity of a further protection 

 against friction ; while it is no doubt immedi- 

 ately the result of the separation of this active 

 cell-growth, alone, or accompanied by fluid 

 derived from the vessels. The bursting of the 

 distended and delicate cell is probably the 

 agent of the separation, and may be due solely 

 to a distention beyond the physical power of 

 resistance which its wall possesses. 



The resistance of the cells on the general 

 or capsular part of the synovial surface, and 

 the irregular and isolated manner in which 

 force detaches them, have been previously 

 noticed, and contrasted with the facility of 

 removing the whole layer of serous cells. 

 They seem to denote, not only a mechanical 

 adaptation to greater friction, but perhaps a 

 corresponding independency of the cells, 

 which possibly form a continuous and active 

 growth, scarcely any two portions of which are 

 exactly of the same age. 



And not only is the secretory activity of 

 these membranes much greater, "but there is 

 every reason to suppose their absorptive func- 

 tions are still more increased. Assuming^ 

 from the preceding appearances of active cell- 

 growth, that a greater quantity of fluid is se- 

 creted by them into the cavity of the joint 

 than the amount of serum which finds its way 

 into the interior of the serous membranes; 

 since only a tolerably uniform and small quan- 

 tity is discovered to be present there, it will 

 follow, that the rapidity of its removal has. 

 corresponded with that of its introduction : 

 and as this removal cannot be attributed to 

 any other cause than that of absorption, we 

 must therefore regard its increase as parallel 

 with the increase of secretion. 



But there is another circumstance which 

 renders it likely that the former of these two 

 processes is even disproportionally greater. 

 However carefully the surfaces of diarthrodial 

 cartilage may be lubricated by the synovial 

 fluid, a very slight knowledge of mechanics 

 would inform us, that some friction of these 

 must of necessity obtain ; and that from the 

 conditions of its density, homogeneous nature, 

 &c., it is probable that the amount of this is, 

 though diminished, yet by no means incon- 

 siderable. So also, from the structure of this 

 substance, it is physiologically probable that 

 its tissue grows towards this surface, and 

 that the arrival of any one particular portion 

 at this point is, mediately or immediately, the 

 cause of the termination of its existence. 

 While the anatomy of this free edge abun- 

 dantly confirms the fact of such an attrition: 

 vertical sections show an irregular border, 

 from which some cells are seen slightly 

 projecting, while others appear (as in/g.402) 

 ground down to its level. 



Whatever be the amount of cartilage 

 which is thus rubbed off' and set free in the 

 cavity of the articulation, or whatever may 

 be the cohesive form which it assumes, the 

 thick and solid cartilaginous lamina which is 

 interposed between this "debris" and the 



M M 



