162 PHILOSOPHY OF ZOOLOGY, 
they are speedily reproduced, and the detached fragments 
even begin to enjoy an independent existence. 
The power of the nervous system to repair the injuries 
it receives, or supply the loss of abstracted portions, has 
been sometimes called in question on very insufficient 
grounds. Its generation at the commencement of life, is 
surely more surprising than its production at an after period. 
But the subject has assumed a character different from 
mere conjecture. |The numerous experiments of SpALLAN- 
zANt and others, to prove the power of reproduction in the 
cold-blooded animals, establish at the same time, the capa- 
bility of the nervous system, in these animals, to reproduce 
abstracted parts. But this power is not confined to cold 
blooded animals. According to the experiments of Mr 
CruicxsHanks * and Dr Haicuron f, portions of the ab- 
stracted nerves of a dog were speedily regenerated, and the 
nerve restored to its ordinary functions. It is probable 
that portions of nerves are generated and destroyed perio- 
dically in those ruminating quadrupeds which have de- 
ciduous horns. 
Are we to conclude, from the view which we have now 
taken, that the parts of the nervous system are homogeneous, 
and susceptible of a certain number of similar functions; that 
the apparently functions of each nerve depend on the organ 
with which it is connected,—to accessary circumstances, 
and not to the nature of the nerve itself? The opposite of 
all this appears to be the case. The nerves which are em- 
ployed in sensation, obviously differ in their mode of ac- 
tion, from those employed for the purposes of volition, and 
hence we may reasonably conclude, that there is a corres- 
ponding difference in structure and composition. The 
same nerve may execute both functions ; but in that case, 


* Phil. Trans. 1795, p. 177, + Ib. p, 190. 
