CXASS I. 1. 3. 9. OF IRRITATION. 33 



others by voiding a great quantity of sand or small calculi. This 

 hardened mucus frequently becomes the nucleus of a stone in the 

 bladder. The salts of the urine, called microcosmic salt, are of- 

 ten mistaken for gravel, but are distinguishable both by their an- 

 gles of crystallization, their adhesion to the sides or bottom of 

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

 Whereas the particles of gravel are generally without angles, and 

 always drop to the bottom of the vessel, immediately as the wa- 

 ter is voided. 



Though the proximate cause of the formation of the calculous 

 concretions of the kidneys, and of chalk stones in the gout, and 

 of the insoluble concretions of coagulable lymph, which are found 

 on membranes, which have been inflamed in peripneumony, or 

 rheumatism, consists in the too great action of the absorbent 

 vessels of those parts; yet the remote causes of these cases is 

 probably owing to the inflammation of the membranes; which 

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

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

 creased action alone without the production of new vessels, which 

 constitutes inflammation. As defined in Class II. 1. 2. 



The fluids secreted from the mucous membranes of animals 

 are of various kinds and consistencies. Hair, silk, scales, horns, 

 finger-nails, are owing to natural processes. Gall-stones, stones 

 found in the intestines of horses, scurf of the skin in leprosy, 

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

 periosteum, which unites broken bones, the calcareous cement, 

 which repairs the injured shells of snails, the calcareous crust on 

 the eggs of birds, the annually renewed shells of crabs, are all 

 instances of productions from mucous membranes, afterwards in- 

 durated by absorption of their thinner parts. 



All these concretions contain phosphoric acid, mucus, and 

 calcareous earth in different proportions; and are probably so 

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

 mode of formation. Some calcareous earth has been discovered 

 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 

 phosphoric acid, and a great quantity of phosphoric acid is shewn 

 to exist in oyster-shells by their becoming luminous on exposing 

 them a while to the sun's light after calcination; as in the expe- 

 riments of Wilson. Botanic Garden, P. 1. Camo 1. 1. 182, note. 

 The exchange of which phosphoric acid for carbonic acid or 

 fixed air, converts shells into lime-stone, producing mountains of 

 marble, or calcareous strata. 

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



VOL II. F 



