ANATOMY OF SEROUS MEMBRANES. 19 



within themselves; and not only so, but it is even possible, and, 

 indeed, is found in morbid dissections, every day, that an organ 

 may be diseased while its serous covering is unaffected; or the 

 reverse. Thus, we have large suppurations in the liver, jvhile its 

 peritoneal coat is healthy; large accumulations of water in the 

 tunica vaginalis testis, while the testicle itself is sound; in the 

 thorax, with sound lungs and heart; in the abdomen, with vis- 

 cera generally sound; in the joints, without an affection of the 

 bones. Nothing is more common than to see partial adhesions, 

 the result of inflammation, causing the opposite sides of these 

 sacs to adhere, without any evident constitutional or visceral 

 derangement; and some of our plans of cure, as in the hydro- 

 cele, are founded upon this well established fact. 



The serous membranes are throughout thin, transparent, 

 and white: in some points their tenuity is so extreme that they 

 seem to consist simply in a smooth, polished surface, spread 

 over parts ; this is strikingly the case on the interior face of the 

 dura mater, on the ventricles of the brain, and on the cartilages 

 of the joints. The evidence of their extension there, is conse- 

 quently derived principally from induction; and from morbid 

 alteration, in which they become thickened. Their internal 

 surface in a natural state, is always smooth, highly polished, 

 shining; and, being also lubricated by its peculiar unctuous se- 

 cretion, the opposite parietes, when they come into contact, 

 glide freely upon each other; a circumstance indispensable to 

 the free action of the joints, and to the peristaltic motion of the 

 bowels. Bordeu has asserted, that these remarkable characters 

 of the serous membranes depend upon the compression and the 

 friction to which they are continually exposed: but to this opi- 

 nion the argument of Bichat is unanswerable, that in their ear- 

 liest observable period in the foetus they have the same polish. 



The fluid secreted from the serous membranes resornbles, 

 strongly, the serosity of the blood. It is poured out continually 

 by the exhalent orifices, and in a short time afterwards is taken 

 up by the absorbents; so that in a natural state there is seldom 

 more than sufficient to lubricate the surface of the membrane. 

 When the abdomen of an animal recently killed is exposed to the 

 air, this fluid rises in the form of a vapour. The several experi- 

 ments, as the application of heat, mineral acids, and so on, which 

 prove the abundance of albumen in the serum of the blood, pro- 



