THE FUNCTIONS OF THE NERVOUS SYSTEM. 
273 
voluntarily abstained from breathing till the lungs were injured. When at 
length no irritation, however violent, can impress the sensorium, the breathing 
ceases and death ensues. The mode of death sufficiently illustrates what is here 
said. We find the intervals of breathing becoming longer before it ceases. 
As the insensibility increases, a greater want of fresh air is necessary to excite 
the patient to inspire, till at length the total privation of fresh air no longer 
producing any sensation, can no longer excite this effort. 
The muscles of respiration then, it would appear, are as perfectly muscles of 
voluntary motion as those of the limbs, and are never excited but by an act of 
the sensorium. When there is no feeling to induce us to breathe, the breath- 
ing ceases. 
That on ordinary occasions we are unconscious of this feeling, in the common 
acceptation of the term, (that is, that it makes no lasting impression on the 
mind, for this is necessary to what we mean by consciousness,) unless the atten- 
tion is particularly directed to it, is no proof that it has not existed. When 
we direct our attention to the act of breathing, especially if we breathe more 
slowly than usual, we can distinctly perceive the sensation which induces us to 
inspire, and that it is a voluntary act which relieves it. 
The same observations respecting consciousness apply to all the more trivial 
habitual acts of the sensorium. In playing on an instrument, we cannot tell 
which finger last struck the chord ; in walking, we cannot tell which leg we 
last moved ; — yet all such acts are strictly acts of volition : when we attend to 
them we can regulate them as we please, but in proportion as they are habitual 
we attend to them the less, and therefore least of all to the act of respiration. 
To the consciousness of having experienced any feeling, it is evident that 
its strength, or some other circumstance attending it, must be such as to im- 
press it on the memory. We are every hour performing many acts of volition 
which are too trivial to be remembered, and consequently at the time we are 
questioned we have no consciousness of their having existed. The proper 
feeling excites the act required, but the feeling is too habitual to command 
the attention. 
It may be difficult for a person not accustomed to reflect on such subjects, 
to believe that every time his leg is moved in walking, he performs a distinct 
act of volition ; but he will be convinced of this if he observes the motions of 
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