SENSATION, 
there is no sensation : where the nervous 
branches are most numerous, there is most 
sensation : if the nerve be destroyed, sen- 
sation cannot be produced from those parts 
to which the nerve belongs which are fur- 
ther from the brain than the injured parts. 
The brain is the ultimate organ of sensa- 
tion of which we have any knowledge. All 
the nerves terminate in the brain. If the 
brain is compressed, sensation is suspended. 
If the brain is considerably injured, sen- 
sation ceases.' — So also, there is considera- 
ble reason to believe that tlie brain is the 
immediate organ of ideas. If the brain is 
^ diseased, many of the phenomena of thought 
are altogether changed j if the brain is com- 
pressed, thought is suspended ; if the brain 
is injured, ideas cease.— So also, the brain 
appears to be the ultimate organ of all mo- 
tions which are not produced by the imme- 
diate action of external objects upon the 
muscles. The muscles are the immediate 
organs of motion. The muscles consist of 
fleshy substances, and sometimes of tendon. 
The tendons fasten the muscles to the 
bones ; and the fleshy part by its contrac- 
tions produces the motions of the bones. 
Into the fleshy parts of the muscles nume- 
rous nerves enter ; they are diffused over 
its surface and within its substance. These 
nerves, as before mentioned, terminate in 
the brain either of the head or back. They 
are the intermediate organs of voluntary 
motion between the brain and the muscles. 
If a nerve be compressed or punctured, 
motion is produced in the muscle over 
which that nerve is distributed. If a por- 
tion of a nerve be cnt or otherwise de- 
stroyed, voluntary motion can no longer 
be produced in that muscle over which it 
was distributed. If the brain be touched 
with any instrument, or caustic applied to 
it, the muscular system undergoes the most 
violent contortions. If the spinal marrow 
be pierced with a probe, all the muscles of 
the trunk and limbs undergo violent con- 
tortions, particularly those of the back. 
If the brain be compressed, the whole body 
becomes paralysed, and the power of volun- 
tary motion is suspended. If the spinal 
marrow be compressed, the power of vo- 
bnitary motion is suspended in those mus- 
cles which receive their nerves from the 
back. If the brain is considerably injured, 
all power of voluntary motion ceases. 
The external organs of sense are usually 
classed under five heads, those of sight, of 
hearing, of feeling, of smell, and of taste. 
The sense of feeling might probably be di- 
vided with convenience into two or three, 
because the classes of sensations, which are’ 
referred to this sense, differ considerably in 
themselves, and in the external causes pro- 
ducing them. But the common arrange- 
ment is sufficient for our purpose. 
By the law of association many ideas 
received directly from sensible objects, 
through the medium of different senses, be- 
come connected, and at last blended toge- 
ther, so as to form one very complex, though 
apparently uncompounded, idea ; and this 
complex idea is often recalled to the mind 
by a corresponding sensation, and, by associ- 
ation, becomes so connected with that sen- 
sation, that the complex idea itself is oftep 
mistaken for a part of the sensation. For in- 
stance, the sensation produced by the im- 
pression made by a globe, on the sense of 
sight, is, as can be proved, nothing more than 
that produced by a circle, with certain varia- 
tions of light and shade j yet, immediately on 
the sensation being perceived, the ideas of its 
solidity, of its hardness, its magnitude, and of 
its being something external to one’s-self, (all 
of which have been derived from the sense 
of touch, in connection with this object or 
others in some respect similar), immedi- 
ately rise up in the mind in one blended 
form ; by their complete coalescence they 
appear to be one, and by their immediate 
and constant connection with the sensation, 
they appear to the mind as a part of the 
sensation. Indeed, there are comparatively 
few people who ever think that the sensa- 
tion derived from the sight is nothing more 
than that derived from a minute picture de- 
lineated on the back part of the eye called 
the retina. Things appear to us, at one 
glance of the sight, to be solid or flat, to be 
near or distant, to be large or small, to be 
conjoined with other things, or separate 
from them, to be parts of our own frame 
or external to it, &c. and all this we appear 
to learn by the sight alone : but the fact is, 
that all these ideas are derived from another 
sense at varions times, and altogether blend- 
ing together, and arising the moment the 
visible impression is communicated, they 
appear part of the visible impression “ The 
visible appearance of objects,” as Berkeley 
observes, “ is a kind of language serving to 
inform us of their distance, magnitude, and 
figure no sooner are these signs pre- 
sented to the mind, than with the rapidity 
of lightning the ideas associated with them 
succeed, and appear to have been commu- 
nicated by the sight, and to be in reahly a 
part of the sensation. 
