150 CHANGES OF BONES. 



tributed, with that nervous energy which is essential 

 to their vitality and to their connexion with other 

 parts of the system. The bones, insensible as they 

 may seem, possess all these attributes of living and 

 organized parts. They are all provided with blood- 

 vessels, with nerves, and with exhaling and absorb- 

 ing vessels ; and they are constantly undergoing the 

 same process of decay and renovation to which all 

 other living parts are subjected. 



That bones are provided with blood-vessels is 

 shown by the fact, that anatomists are able to trace 

 these vessels into their substance, and to inject 

 those of a young subject with wax, so minutely as 

 to make the bones appear of a lively red colour. 

 That they are provided also with nerves is evident, 

 both from dissection and from the effects of in- 

 juries and disease. A healthy bone may be cut or 

 sawn across without causing pain, but when the 

 same bone becomes inflamed, the most excruciating 

 torture is felt. And as sensation is the exclusive 

 attribute of the nervous system, this fact alone 

 would authorize us to assume their existence, even 

 although nervous fibres could not be traced entering 

 the osseous substance. 



That the substance of the bones is continually 

 undergoing a change, and that, while the old parti- 

 cles are withdrawn by absorbents, new particles are 

 constantly deposited by the nutrient or exhalant ves- 

 sels, is abundantly proved by the often repeated ex- 

 periments of Duhamel. If madder be mixed with 

 the food of fowls for a few days, and the fowls be 

 then killed, the colouring matter deposited by the 

 nutrient vessels will invariably be found to have 

 died the bones of a deep red ; and if the madder be 

 withdrawn, the bones will then be found to be less 

 and less red in proportion to the length of time 

 which has been allowed to elapse evidently showing 

 that waste and renovation are constantly going on. 



It may be thought, that bones are, in their very 



