REGENERATION OF BONE. 183 



parts. Thus it was long since proved by the experiments of Hales and 

 Hunter, that the growth of a long bone takes place chiefly towards the 

 extremities ; for they found that, when metallic substances were inserted 

 in the shaft of a growing bone of a young animal, the distance between 

 them was but little altered after a long interval, whilst the space be- 

 tween the extremities of the bone had greatly increased. And it seems 

 that, at a later period, when the epiphyses have become completely 

 united to the shaft, an elongation continues to take place, by the slow 

 ossification of the articular- cartilage. Again, the bone is progressively 

 increased in thickness, by the gradual production of new osseous matter 

 upon its surface ; this production being effected by the conversion of 

 the inner layer of the periosteum, the fibres of which are found to be 

 continuous with those of the animal matrix of the surface of the bone. 

 And it is by the successive formation of new layers of osseous tissue, 

 one within another, giving the appearance of concentric rings when the 

 Haversian canals are cut across (Fig. 49), that the proportion of hard 

 to soft parts in bone is gradually increased ; the calibre of the Haver- 

 sian canals being correspondingly diminished. Of this we have a 

 curious exemplification in the antlers of the deer, in which the cavity 

 of the canals is gradually choked up by the formation of osseous 

 tissue, until the vascular supply is cut off, and the death of the bone is 

 the result. 



306. The difference in the relations of the Osseous substance to the 

 vascular network, at different ages, accounting for the variations in the 

 rapidity of its nutrition and reparation, is well displayed in the effects 

 of Madder. This substance has a peculiar affinity for Phosphate of 

 Lime ; so that when the latter is formed by precipitation in a fluid 

 tinged with madder, it attracts colour to it in its descent, and falls to 

 the bottom richly tinted. Now when animals are fed with this sub- 

 stance, it is found that their bones become tinged with it, the period 

 required being in the inverse proportion to their age. Thus in very 

 young animals a single day suffices to colour the entire skeleton, for in 

 them there is no osseous matter far from the vascular surfaces ; when 

 sections are made, however, of the bones thus tinged, it is found that 

 the colour is confined to the immediate neighbourhood of the Haversian 

 eanals, each of which is encircled by a crimson ring. In full-grown 

 animals, the bones are very slowly tinged ; because the osseous texture 

 is much more consolidated and less permeable to fluid than in earlier 

 life ; and because the vascular membrane lining the Haversian canals 

 is removed further from the outer and older layers of osseous tissue 

 which surround them, by the interposition of newer concentric layers, 

 which diminish the diameter of the canals. In the bones of half-grown 

 animals, a part of the bone is nearly in the perfect condition, while a 

 part is new and easily coloured ; so that the action of this substance 

 enables us to distinguish the new from the old. 



307. The Regeneration of Bone, after loss of its substance by disease 

 or injury, is extremely complete ; in fact there is no other structure of 

 so complex a nature, which is capable of being so thoroughly repaired. 

 Although the regenerative power appears to be so much less in Verte- 

 brated animals, than it is in the lower Invertebrata, yet it is probably 



