248 MANUAL OF HISTOLOGY. 



is found taking a far more subordinate position, and the amount of 

 fluoride of calcium is still less. The admixture, finally, of magnesia 

 appears quite inconsiderable in comparison to the abundant occurrence of 

 the lime salts ; it is supposed generally, and rightly, to occur in the form 

 of a phosphate. 



Besides these, we meet with alkaline salts, with phosphoric acid, in 

 fresh bone ; also chlorine (sulphuric acid ?), iron, manganese, and silica, 

 which may be set down as belonging to the nutritive fluid saturating the 

 tissue. 



By means of calcining, the organic substratum may be removed from 

 bone without destroying its form. But when thus treated, the tissue loses 

 all cohesion, and breaks up into a white powdery mass on being handled. 

 If we accept it as a fact that no equivalent combination of phosphate of 

 calcium with glutin exists, that the proportion of bony earths in the several 

 bones varies considerably, and that the mineral constituents may be ex- 

 tracted from osseous tissue without the slightest injury to its texture, we 

 must see that the combination of bony earths with the so-called bone- 

 cartilage is probably only mechanical. And yet the granular deposit of 

 lime-salts in cartilage undergoing calcification, compared with the diffuse 

 deposit in true osteogenic tissue from the very commencement, ia some- 

 what puzzling. 



The following are the results of two analyses, by Heintz, of the compact 

 tissue of a female tibia : 



1. 2. 



Phosphate of calcium, . 85'62 85 -83 



Carbonate of calcium, - ir ; 9'06 9*19 



Fluoride of calcium, .' 3 '57 3-24 



Phosphate of magnesium, . T75 1-74 



As is usually admitted, the bony earths vary, first of all, according to 

 the portion of the skeleton in one and the same body subjected to analysis. 

 Thus Rees obtained as a maximum 63'50 from the temporal, and the 

 smallest amount from the scapula, namely, 54*51 per cent. (2). Bibra 

 found the highest figures in the femur, and the lowest in the sternum, the 

 numbers being respectively 69 and 51 per cent. Compact osseous tissue 

 is in general richer in bony earths than the spongy kind, probably 

 because the latter can be but imperfectly freed of the soft parts enclosed 

 in it. 



Further, the same portion of bone is said to change with age ; for at 

 an early period it appears to be richer in organic material than at a 

 later. Thus Bibra found in the femur of a foetus seven months 

 old, 59-62 per cent, of bony earths ; in that of an infant of nine months, 

 56.43 ; in that of a child at five years, 67'80 ; in a man of twenty-five 

 years old, 68-97; in a woman of sixty-two, 69 -82; and in another of 

 seventy-two years of age, 66*81. 



It is an interesting and not yet satisfactorily explained fact, that fossil 

 bones are very rich in fluoride of calcium. The latter may rise as high as 

 10 or even 16 per cent, of the ash in quantity. 



REMARKS. 1. The theory of the transformation of chondrigen into collagen duriner 

 the process of ossification (p. 22), which formerly occupied the attention of chemists 

 ami physiologists to a great extent, has almost lost all worth since the investigations 

 of Bruch and //. Muller on the subject. We now know that cartilage is not metamor- 

 phosed into bone, but is dissolved, so making room for the development of osseous 



