ii2 THE CHEMISTR Y OF THE TISSUES AND ORGANS. 



From a large number of analyses, Hoppe-Seyler gives the following 

 figures representing percentages of the total ash : 



Ca. P0 4 . CO,. Fl. Mg. Cl. 



38-49 54-46 6-24 1-28 0-44 0-19 



From his own numbers, Zalesky has calculated the probable composition 

 of the mineral constituents of bone as follows : 



Calcium phosphate . . . 83 '889 



carbonate . . . 13 -03 2 

 Calcium in combination with fluorine, 



chlorine, etc. .... 0*350 



Fluorine 0-229 



Chlorine . . ^ . . . 0-183 



Hoppe-kSeyler considered that the characteristic inorganic ingredient of 

 bone, dentine, and enamel is one analogous to apatite. Apatite has the 

 formula Ca 10 Fl 2 (P0 4 ) G , or Ca 10 Cl. 2 (P0 4 ) 6 . Very small quantities of these 

 substances, however, occur in bone ; the chief compound is one in which C0.j 

 takes the place of the F1 2 or C1 2 , namely, Ca 10 C0 3 (P0 4 ) G . See, however, 

 Gabriel's researches below. 



Tooth. The calcareous tissues of tooth are dentine, enamel, and 

 crusta petrosa. The last named is bone ; dentine is chemically similar 

 to bone. Enamel, though epithelial in origin, may be conveniently 

 taken here. 



Dentine. This consists of water 10 per cent., and solids 90 per cent. 

 The solids are organic and inorganic. The organic solids are less 

 abundant than in bone. They consist of collagen and elastin ; the latter 

 form the lining of the dentinal tubules. From Aeby's analyses, Hoppe- 

 Seyler gives the following table : 



Ca 1() C0 3 (P0 4 ) 6 . . . 72-06 per cent. 

 MgH(P0 4 ). . . . 0-75 



Organic substances . . 27*70 ,, 



Enamel. This is the hardest tissue in the body. Hoppe-Seyler 's 

 quantitative analyses give the following mean result : 



Ca 10 C0 3 (P0 4 ) ( . . . . 96-00 per cent. 

 MgHPO 4 . . . .1-05 

 Organic substances . . 3 '60 ,, 



Various other investigators give numbers varying from 2 to 10 per 

 cent, of organic matter. This they estimate by loss on ignition. Tomes, 1 

 however, has recently shown that this loss is chiefly if not wholly due 

 to water. On attempting to estimate the organic matter directly, 

 none was found, or a quantity too small to be weighed. 



Gabriel 2 has recently worked at the question of the constitution of 

 the mineral matter of bones and teeth. Some of his conclusions do 

 not accord with the older work of Hoppe-Seyler. He finds that the 

 constituents are water, lime, magnesia, potash, soda, phosphoric acid, 

 carbonic anhydride, chlorine, and fluorine. The quantities of lime 

 and phosphoric acid, which are the most abundant constituents, vary 



1 Journ. PhysioL, Cambridge and London, 1896, vol. xix. p. 217 ; Trans. Odont. Soc. 

 Gr. Brit., London, 1896. p. 114. 



2 Ztschr. f. physiol. Chem., Strassburg, Bd. xviii, S, 257, 



