168 Mr. Bell on the nervous circle which connects 
not a conductor towards the brain, and that it cannot perform 
the office of a sensitive nerve. 
Without attempting to determine the cause, whether de- 
pending on the structure of the nervous cord, or the nature, 
or the source of the fluid contained, a pure or simple nerve 
has the influence propagated along it in one direction only, 
and not backwards and forwards ; it has no reflected opera- 
tion or power retrograde ; it does not both act from and to 
the sensorium. 
Indeed reason without experience would lead us to con- 
clude, that whatever may be the state, or the nature of the 
activity of a motor nerve during exertion, it supposes an 
energy proceeding from the brain towards the muscles, and 
precludes the activity of the same nerve in the opposite 
direction at the same moment. It does not seem possible 
therefore that a motor nerve can be the means of communi- 
cating the condition of the muscles to the brain. 
Expose the two nerves of a muscle ; irritate one of them, 
and the muscle will act ; irritate the other, and the muscle 
remains at rest. Cut across the nerve which had the power 
of exciting the muscle, and stimulate the one which is undi- 
vided — the animal will give indication of pain ; but although 
the nerve be injured so as to cause universal agitation, the 
muscle with which it is directly connected does not move. 
Both nerves being cut across, we shall still find that by 
exciting one nerve the muscle is made to act, even days after 
the nerve has been divided ; but the other nerve has no 
influence at all. 
Anatomy forbids us to hope that the experiment will be 
