$36 OF QLANDS AND MEMBRANES. SLCT. XXVI. 3. 



jned ftate they have the greateft fenfibility to pain, 

 as in the pleurify and paronychia. 



3. On all thefe membranes a mucilaginous or 

 aqueous fluid is fecreted, which moiftens and lubri- 

 cates their furfaces, as was explained in Section 

 XXIII. 2, Some have doubted, whether this mu- 

 cus is feparated from the blood by an appropriated 

 fet of glands, or exudes through the membranes, 

 or is an abrafion or deftruction of the furface of the 

 membrane itfelf, which is continually repaired on 

 the other fide of it, but the great -analogy between 

 the capillary veflels, and the other glands, counte- 

 nances the former opinion ; and evinces, that thefe 

 capillaries are the glands, that fecrete it ; to which 

 \ve mutt add, that the blood in patting thefe capil- 

 lary veflels undergoes a change in its colour from 

 florid to purple, and gives out a quantity of heat ; 

 from whence, as in other glands, we muft conclude 

 that fomething is fecreted 'from it. 



III. The feat of rheumatiirn is in the membranes, 

 or upon them ; but there are three very diftinct dif- 

 eafes, which commonly are confounded under this 

 name. Firft, when a membrane becomes affected 

 with torpor, or inactivity of the veflels which com- 

 pofe it, pain and coldneis fucceed, as in J:he hemi- 

 crania, and oiher head-achs, which are generally 

 tefmed nervous rheumatifm ; they exift whether 

 the part be at reft or in motion, and are generally 

 attended with other marks of debility. 



Another rheumatifm is faid to exift, when inflam- 

 mation and fweliing, as well as pain, affect fome of 

 the membranes of the joints, as of the ancles, 

 wrifts, knees, elbows, and fometimes of the ribs. 

 This is accompanie4 with fever, is analogous to 

 pleurify and other inflammations, and is termed the 

 pcute rheumatifm. 



A third difeafe is called chronic rheumatifm, 

 is d$inguiJhed from that firft mentioned, as 



JB 



