TUB SKELETON. 27 



tion of soluble salts to the less soluble phosphates of lime is greatest 

 in the fish, and that there is most carbonate of lime in the bones of 

 the tortoise. The quantity of evaporable fluid is greatest in the 

 bones of Fishes, especially in those of the semi-osseous sharks and 

 rays, in the skeletons of which also the salts of soda are in larger 

 proportion than in the osseous fishes. The animal part of the 

 shark's skeleton difliers from tlie glutin of ordinary bones, and from 

 the ossifiable cartilage of higher animals ; it has more analogy 

 with mucus, I'equiring 1000 times its weight of boiling water for 

 its solution ; and this is neither precipitated by infusion of galls, nor 

 yields any gelatine upon evaporation. In the entirely unossified 

 skeleton of the lamprey Bibra found only 1^ per cent, of eai'thy 

 salts. 



How, we may next ask, are the inorganic earthy particles diffused 

 tlu'ough the animal basis, and whence are they obtained ? Bones are 

 not a primitive formation, but the result of a transmutation of pre- 

 existing tissues. The inorganic salts defined in the foregoing tables 

 pre-exist in the albumen of the egg, in the milk which nourishes the 

 new-born mammal, in the plasma or " liquor sanguinis " of the circu- 

 lating fluids. 



The blastema or primitive basis of bone is not originally cartilage, 

 but more resembles mucus in its chemical characters : it appears at 

 first to be a sub-transparent glairy fluid, but contains a multitude of 

 minute corpuscles. Its assumption of the cartilaginous character and 

 consistency is attended with the appearance in it of numerovxs small, sub- 

 elliptic, nucleated cells. As the cartilage hardens, these cells increase in 

 number and size, and begin to accumulate, and to be arranged in 

 linear series at the part where ossification is about to commence. 

 These series in the cartilage of long bones are usually vertical to its 

 ends, and in flat bones are vertical to the peripheral edge ; ^. e. 

 they are parallel to the axis of the long bone, and are radiated in the 

 flat one, but not with mathematical exactness. 



The nucleated cells are the instruments by which the earthy par- 

 ticles are arranged in order ; and, in bone, as in tooth, there may 

 be discerned in this predetermined arrangement, the same relation 

 to the acquisition of strength and power of resistance, with the 

 greatest economy of the building material, as in the disposition 

 of the beams and columns of a work of human ai-chitecture. (v. 

 p. vi.) 



The poAver of the cells so to operate upon the salts of the plasma, 

 which percolates the intervening tissue, seems to reside chiefly in tlie 

 repellent property of their nuclei : I have been led by observation of 



