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



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

 hardened mucus frequently becomes the nucleus of a (tone in the 

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

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

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

 the pot, and by their not being formed till the urine cools. Where- 

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

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

 voided. 



Though the proximate caufe of the formation of the calculous 

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

 of the infoluble concretions of coagulable lymph, which are found 

 on membranes, which have been inflamed in peripneumony, or 

 rheumatifm, coniifts in the two great action of the abibrbsnt 

 veflels of thofe parts 5 yet the remote caufe in thefe cafes 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 vefTels,which 

 conftitutes inflammation. As defined in Clafs II. 1. 2. 



The fluids fecreted from the mucous membranes of animals 

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

 hnger-nails, are owing to natural proceffes. Gall-ftones, ftones 

 found in the inteflines of horfes, fcurf of the fkin in leprofjr, 

 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 fhells of crabs, are ail in- 

 ffances of productions from mucous membranes, afterwards in- 

 durated by abforption of their thinner parts. 



All thefe concretions contain phofphoric acid, mucus, and 

 calcareous earth in different proportions 5 and are probably fo 

 far analogous in refpecf. to their component parts as -well as their 

 mode of formation. Some calcareous earth has been difcovercd 

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

 Elements of Practice. A little calcareous earth was delected 

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

 phofphoric acid, and a great quantity of phofphoric acid is (hewn 

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

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

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

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

 or fixed air, converts fhells into lime-done, producing mountains 

 of marble, or calcareous flrata. 



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



Vol. II. F evesj 



