CLASS I. i. 3. 9. OF IRRITATION. 33 



others by voiding a great quantity of fond, or fmall calculi. This 

 ned mucus frequently becomes the nucleus of a ftone in the 

 bladder. The falts of the urine, called microcofmic fait, are of- 

 ten iniftaken for gravel, but are diftinguifhable both by their an- 

 gles of cryftallization, their adhefion to the fides or bottom of 

 the pot, and by their not beingformedtill the urine cools. Where- 

 as the particles of gravel are generally without angles, and always 

 drop to the bottom of the veflel, immediately as the water is 

 voided. 



Though the proximate caufe of the formation of the calculoua 

 concretions of the kidneys, and of chalk-ftones in the gout, and 

 of the infoluble concretions of coagulable lymph, which are found 

 on membranes, which have been inflamed in peripneumony, or 

 rheumatifm, confifts in the two great action of the abforbent 

 veffels of thofe parts ; yet the remote caufe in thefe cuies is 

 probably owing to the inflammation of the membranes ; which 

 at that time are believed to fecrete a material more liable to co- 

 agulate or concrete, than they would otherwife produce by in- 

 creafed action alone without the production of new veflels,which 

 conftitutes inflammation. As defined in Glafs II. I. 2. 



The fluids fecreted from the mucous membranes of animals 

 are of various kinds and confiftencies* Hair, filk, fcales, horns, 

 finger-nails, are owing to natural proceflfes. Gall -ftones, ftones 

 found in the interlines of horfes, fcurf of the {kin iii leprofy, 

 ftones of the kidneys and bladder, the callus from the inflamed 

 periofteum, which unites broken bones, the calcareous cement,- 

 which repairs the injured (hells of fnails, the calcareous cruft on 

 the eggs of birds, the annually renewed melts of crabs, are all in- 

 ilances of productions from mucous membranes, afterwards in- 

 durated by abforptioxi of their thinner parts. 



All thefe concretions contain phofphoric acid, mucus, and 

 calcareous earth in different proportions ; and are probably fo 

 far analogous in refpect to their component parts as well as their 

 mode of formation. Some calcareous earth has been difcovered 

 after putrefaction in the coagulable lymph of animals. Fordyce's 

 Elements of Practice. A little calcareous earth was detected 

 by Scheele or Bergman in the calculus of the bladder with much 

 phofphoric acid, and a great quantity of phofphoric acid is fhewn 

 to exift in oyfter-fhells by their becoming luminous on expofmg 

 them a while to the fun's light after calcination ; as in the ex- 

 periments of Wilfon. Botanic Garden, P. i. Canto i. 1. 182, 

 note. The exchange of which phofphoric acid for carbonic acid,- 

 or fixed air, converts (hells into lime-ftone, producing mountains 

 of marble, or calcareous ftrata. 



Now as the hard lumps of calcareous matter, termed crabs' 

 Vol. II. F eyes, 



