ANIMALS AND VEGETABLES. 45 
confined to certain organs, and certaim conditions of these 
organs. If the nerves of the finger are cut across or 
compressed, I am unable to communicate to my finger the 
requisite power. Sensation has ceased, and along with 
it, voluntary motion. In the one case, the sensation, by 
the ligature or division of the nerve, is prevented from as- 
cending; in the other, the excitement to voluntary motion 
is prevented from descending, by the iterposition of the 
same means. I conelude, therefore, that the presence of 
the nerves is essentially necessary to voluntary motion. 
Here, however, there is another condition necessary. ‘The 
organs to which the nerves proceed, must be so construct- 
ed as to admit of motion. My fingers possess this requisite 
qualification in an eminent degree ; but when many other 
parts of my body are touched by any object, even though I 
feel its presence, I cannot move away the part without a ge- 
neral movement of the whole body. In many cases, I cannot 
even accomplish my object by any movement of the body, as 
when the substance is situated in some central part, so con- 
structed as not to obey the will, as is the case with gouty 
or urinary concretions. Voluntary motion, then, depends 
on the presence of nerves, and the structure of the parts to 
which these are distributed. 
As all animals may be considered as possessing nerves, 
and consequently, the essential requisite of voluntary mo- 
tion; the organs of animals are likewise so constructed, 
as to admit of its display in the variety of actions which 
they perform. In a few animals, however, such as the 
sponge, the displays of this power are scarcely discernible. 
But as in all such animals there are some soft parts, and: 
as they all possess nerves, we may infer from analogy the 
existence of this faculty, although its operations are imper- 
ceptible to our senses. 
