SECT. XXVI. 2. OF GLANDS AND MEMBRANES. 335 



II. r. The whole fur face of the body, with all 

 its cavities and contents, are covered with mem- 

 brane. It lines every vefiel, forms every cell, and 

 binds together all the mufcular and perhaps the 

 o(Teo.us fibres of the body ; and is itfelf therefore 

 probably a fimpler fubftance than thofe fibres. And 

 as the containing vefTels of the body from the 

 larged to the lead are thus lined and connected 

 with membranes, it follows that thefe membranes 

 themfelves confided of unorganized materials. 



For however fmall we may conceive the diame- 

 ters of the minuted vefTels of the body, which 

 efcape our eyes and glafles, yet thefe vefleis mud 

 coniid of coats or fides, which are made up of an 

 unorganized material, and which are probably pro- 

 duced from a gluten, which hardens after its pro- 

 duction, like the filk or web of caterpillars and 

 fpiders. Of this ntaterial confid the membranes, 

 which line the fhells of eggs, and the (hell itfelf, 

 both which are unorganized, and, are formed from, 

 mucus, which hardens after it is formed, either by 

 the abforption of its more fluid part, or by its uni- 

 ting with forne part of the atmofphere. Such is 

 alfo the production of the fhelis of fnails, and of 

 ihell-nfh, and 1 fuppole of the enamel of the 

 teeth. 



2. But though the membrane?, that compofe the 

 fides of the mod minute velTels, are in truth unor- 

 ganized materials, yet the larger membranes, which 

 are perceptible to the eye, feem to be compofed of 

 an intertexture of the mouths of the abforbent 

 fydem, and of the excretory du&s of the capilla- 

 ries, with their concomitant arteries, veins, ?Uld 

 nerves: and from this conftruction it is evident, 

 that thefe membranes mud poiTefs great irritability 

 to peculiar dimuli, though they are incapable of 

 any motions, that are vifible to the naked eye : 

 daily experience mews us, that in their infla- 



