Another mode of nervous action, but having less dependence on the brain than those just considered, is termed reflex. This action is a peculiar function, of the spinal cord, and prolongs, the natural movements of muscles associated for certain definite purposes, as of locomotion; and when they are once set in operation, do, by so slight a degree of sensation that it makes no impression on the sensorium commune, continue to operate in the direction of the impulse, until changed by a mandate of the will, or arrested by physical obstruction,

A good example of reflex and associate action occurs in the act of swallowing. When a morsel of food is carried so far back in the mouth as to impress the sensitive nerves of the fauces, the muscles of deglutition are immediately aroused, and not only act independently of the will, but they require its strongest effort to resist their movement if desired. Now, such action being independent of volition, it may, when once called into play, be continued by causes that do not affect the brain; and, consequently, when a consecutive train of action is started, it may be prolonged independently of the will. This state may occur as well during sleep as in vigilance, for we know that the action of the muscles of organic life is maintained in sleep by this process; the blood is propelled by the heart, and respiration by the associate action of the muscles of the chest.

The medulla oblongata is the seat of sensation and reflex action. Without the cerebrum animals will fly and walk, and yet appear as though asleep. Among the experiments of M. Flourens, we find that "an animal, in which the cerebral hemispheres have been removed, is in a state of stupor, but presents, nevertheless, manifest signs of sensibility, and not merely of the reflection of impressions. It no longer performs any Voluntary movements, but, when struck, it has all the manner of an animal waking from sleep. In whatever position it be placed it resumes the equilibrium. If laid upon the back, it rises again; if pushed, it walks. If it be a bird, and we throw it up into the air, it flies; if it be a frog, it leaps when touched. The animal has, doubtless, lost, its memory, it no longer reasons; but, nevertheless, it feels, and the sensations excite in it movements which are different from the phenomena of mere nervous reflection. Cuvier very aptly compares animals in this condition to a sleeping man; he also seeks an easy position - he feels."