OF THE SEROUS MEMBRANES IN GENERAL. 151 



ly thin that they penetrate into the membrane itself. The 

 nerves of the serous membranes are not known. 



188. The liquid contained in these membranes is not the 

 same in all; it resembles however more or less the serum of 

 the blood or blood deprived of its colouring matter. It con- 

 tains, in general, water, albumen, an incoagulable matter that 

 may be considered a sort of gelatiniform mucus, a fibrous 

 matter and soda. We shall see hereafter the difference pre- 

 sented by this liquid in the various species of the serous 

 membranes. 



189. The serous membranes, during life particularly, are 

 highly extensible and retractile, as is seen in dropsies and 

 after the disease is cured: but their enlargement is not always 

 the result of their extensibility; their folds disappear, which 

 being gradually developed, serve to aid the increase of the 

 membrane. Another cause which assists in this augmenta- 

 tion of volume, is the sliding of which this is susceptible, the 

 species of locomotion it experiences when it is distended in 

 one part only, as is particularly seen in hernia. There appears 

 also in some cases a real increase of nutrition, which contri- 

 butes to the production of this phenomena : this augmentation, 

 with the other causes of ampliation is manifested in pregnan- 

 cy. These phenomena are not all equally marked in the 

 different species of serous membranes: the peritoneum pre- 

 sents them in the highest degree; they are much less so in the 

 synovial membranes, the articulating ones particularly, which 

 partly arises from the less extensible nature of these mem- 

 branes, and from their having fewer folds, and above all from 

 their connexions which do not permit them to displace them- 

 selves with the same facility. When the distension has ceased 

 they gradually return to their original state, but if it has pro- 

 ceeded to a very relaxed state, traces of it always remain. 



190. The force of formation, tolerably well developed in 

 the serous membranes, is less so in them, however, than in the 

 free cellular tissue. Their mobility is very limited, extending 

 only to the feeble degree which constitutes tonicity. But if 

 irritation does not occasion in them any perceptible move- 

 ments, it develops sensibility there: in fact these membranes 

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