TEETH, SKIN, ETC. 1057 



peculiar, it contains 8 proportions of lime to 3 of phosphoric 

 acid, or 8CaO-|-3PO 5 ; but it is undoubtedly a compound of two 

 tribasic phosphates of lime, namely, 2CaO,HO,PO 5 -{- 

 2(3CaO,PO 5 j ; containing* 1 atom of water before calcination- 

 The proportion between the earth and cartilage varies in dif- 

 ferent bones; the human scapula has been found to contain 54|, 

 the temporal bone 63j per cent of bone-earth. Human bones 

 well dried are said to contain 1 1 per cent of carbonate of lime^ 

 which is three times the quantity in the bones of the ox. Fluo- 

 ride of calcium is also found in bones, although not uniformly 

 present according to Dr. Rees' observations. The salt in ques- 

 tion occurs in fossil bones, and is contained in considerable 

 quantity in the human bones found in Herculaneum. In weak 

 or ricketty bones the proportion of bone earth has been found 

 diminished by 14 per cent. M. Valentin finds, by the analysis 

 of morbid osseous formations, that the callus and exostosis 

 contain more carbonate of lime than the sound bone upon which 

 they form, and that, on the contrary, the caries contains a quan- 

 tity of carbonate of lime smaller by several per cent than the 

 sound bone. 



The teeth are composed of the same materials as bone, but 

 contain less cartilage ; usually about 64 per cent of phosphate 

 of lime, about 6 per cent of carbonate of lime with carbonate of 

 magnesia, and 28 per cent of cartilage. The ivory of the teeth 

 contains no cartilage, about 88 per cent of phosphate of lime, 

 with some fluoride of calcium, and 10 per cent of carbonate of 

 lime, with magnesia. The antlers of deer have the same compo- 

 sition as bone. 



Skin. The cuticle or epidermis is a coating of horny matter 

 (page 1039), without blood-vessels. The mucous membrane 

 (rete Malpighi], between the cuticle and true skin, appears to 

 consist of the matter of the epidermis not yet hardened. The 

 corium or true skin is completely decomposed by digestion in 

 boiling water, and yields a solution of gelatin (page 1036). The 

 composition and peculiar characters of the organic matter in 

 nails, claws, hoofs, hair, wool, and feathers, have already been 

 described (pages 1041, 1042). All these substances contain, be- 

 sides, from ^ to 2 per cent of bone-earth. 



Human perspiration has an acid re-action, it is supposed from 

 acetic acid, but from its observed effects upon the dyed colours 



2 z z 



