Now when the brain’s influence is kept from muscle, that muscle will still possess _irritability_, derived from the spinal marrow; nay, that irritability will be greater, _because it has not been expended_ by the acts of that volition, which resides solely in the brain, and which is now cut off. Thus the _excito-motory_ function, and the influence of volition, are in these cases _antagonists_. And this principle of the _incident_ and _reflex spinal_ nerve is an explanation of the curious dilemma, regarding the suspension of the will in sleep and dream, to which Dr. Stewart alludes.—“Not a suspension of volition, but only of _its influence_ over those organs, which it moves when we are awake.” Decide for yourselves between the physical and metaphysical theories. Yet, do you not see that all this does not essentially require the direction of mind? If you tickle the palm of a sleeping child, it will close its hand upon your finger; if you awake it, and _engage its attention, it will often leave its hold_. This is a fact proved by the _anencephalous_ or brainless children. Even the puppy, deprived of its brain, and also the _mammary fœtuses_ of the kangaroo and opossum, fix eagerly on the nipple when it touches their lips. There is a beautiful mechanism in the foot of the roosting birds, adapted to this physiological law. The tendon of the claws is tightened immediately they are touched, by which action they contrive to grasp the bough or perch even when asleep. In cases of _paralysis_ even, the foot will sometimes be instantly drawn up, although it does not possess the least sensation; we may assert, then, that irritability is in an _inverse ratio_ to sensibility. The _polype_, in which we trace no brain or nerve, exists and moves by its irritability, and without sensation or consciousness. We know also that the _vis insita_, or _vis nervosa_ of a muscle, that is, its irritability, exists even after the animal life has ceased. The turtle will live and move long after its brain has been removed. The heart itself, an involuntary muscle, is stimulated also to action without sensation. The heart of the assassin, Bellingham, beat long after he was cut from the gallows. If I have made these things clear, I am now prepared to explain, with some anticipation, those two curious contrasts, somnambulism and incubus. If the spinal or motive nerves be asleep, and the cerebral or intellectual, or volition nerves, awake, we shall have night-mare; if, on the contrary, the motive nerves are in excess, beyond the sensiferous or volition nerves, we have sleep-walking. ASTR. I believe the philosophy of Leibnitz affirms _two_ perceptions; one with, and another without, consciousness. I do not recollect if he distinguishes the _seat_ of these _perceptions_; but, if the brain be that which perceives, I presume consciousness will follow that perception sometimes in so slight a degree as not to excite judgment or reflection. Am I correct?