90 NERVOUS SYSTEM. 



the nervous medulla, than the pia mater has in \secreting 

 the substance of the brain. 



Q. Does the brain supply the nervous medulla? 



#. On the contrary, it has been just said that the me- 

 dulla is deposited by the arteries of the nerve. 



Q. What pathological facts does this arterial nutrition 

 of the nerves explain ? 



Ji. It accounts for the preservation of the inferior por- 

 tion of a cut nerve; for the continued nutrition of a nerve 

 from which cerebral communication has been cut off by 

 ligature; and for the uninterrupted support of a nerve, 

 which, in palsy, may have ceased to correspond with the 

 brain. The secretion of nervous medulla, and the nutri- 

 tion of nervous organization by the arteries, explain these 

 facts. 



Properties of the Nervous System of Animal Life. 



Q. Do the nerves manifest much textural property ? 



<&. They do not. If extension be suddenly made, it is 

 dangerous, but if gradually applied, it is borne to a consi- 

 derable degree. The nerves possess little contractility of 

 texture. 



Q. How is nervous sensibility divided? 



Jl. Into inherent and common. 



Q. In what part of a nerve does animal sensibility re- 

 side? 



fl. In the medullary substance; the nervous coat has 

 very little. This medullary substance has animal sensi- 

 bility to a very great degree. 



Q. Why are nerves not painful when surrounded by 

 fluids, tumours, or when exposed to the air? 



