SECT. 107.] OSSEOUS SYSTEM. 207 



finest particles more necessary than here. There cannot be a doubt 

 that the fluids, which this ' plasmatic vascular system ' (Leasing) 

 of the bones — which according to our present views, must be 

 regarded as a network of stellate cells — receives from the blood- 

 vessels, modified by the vital processes in the nucleated cells of 

 the lacunae, are indispensably necessary for the maintenance of 

 the bones, for we see that when the vascular supply of a bone is 

 cut off or impeded by the destruction of the periosteum or of the 

 marrow, by the tying of the vessels of a limb, by obliteration of 

 the periosteal vessels by pressure from without (aneurism, morbid 

 growths), a necrosis of the parts concerned is the sure consequence. 

 This, according to Virchow, frequently affects only the substance 

 within the province of one or some few cells ; nevertheless, the 

 active collateral circulation (see above) is scarcely ever able to 

 prevent it. On the other hand, we are not as yet able to say how 

 the plasma of the bones circulates ; for a movement of it from one 

 set of vessels to another (probably from the more arterial through 

 several lamellae to the venous) must, doubtless be assumed ; nor 

 do we know in what actual changes the nutrition of the osseous 

 tissue consists ; and this more especially, because the chemical in- 

 vestigation of the process, and particularly of the organic products 

 of the decomposition of bone is still very defective. 



That the tissue of the bones is in a state of continual, and, indeed, 

 very energetic change, is evinced not only by their various diseased 

 conditions, but by the alterations they undergo in old age. At 

 this period, extensive absorption of bone takes place, as well 

 externally as internally ; an example of the former is furnished 

 by the alveolar processes of the jaw, which are wholly removed; 

 of the latter by the increased porosity and brittleness of every 

 description of bones, as the cylindrical bones, and those of the 

 skull, by the enlargement of vascular openings (vertebrae, apo- 

 physes) and by the greater roughness of the surfaces of bones. 

 To this senile atrophy of the bones a consecutive new formation 

 of bone in the interior may be super-added, a so-called sclerosis, 

 as in the flat cranial bones, by which means, in direct opposition 

 to the other phenomena of senile bones, the diploe disappears, its 

 spaces becoming filled with new r osseous substance, the venous 

 spaces and emissories being obliterated, and the entire bone 

 becoming heavier. 



From the vascularity of the bones, and their active elementary 

 changes, it cannot be surprising that they are so richly provided 

 with nerves. Of these, the main function is, in my opinion, to 



