Animal Magnetism, as connected with the phenomena of sleep, is not only interesting as a matter of metaphysical speculation, but of great importance in the illustration of our subject. In truth, sleep is always the same in principle, though differing in degree, let the inducing cause be what it may ; and that condition which the disciples of Mesmer term Magnetic sleep, is but its most profound state, or the stage of torpor.

The phenomena presented by the power of the mesmerizer in opening a passage to the mind in this isolated condition, displaying its integrity in a light so clear that we perceive its condition and power of action to be as perfect during sleep, while the external senses are sealed to their natural stimuli, as when it receives its impressions through their media, - are truly wonderful. It acknowledges an unusual channel of communication when its ordinary ones are closed, and as the sequel will show, is ever perfect, and ready to reply to impressions when correctly made.

The manipulations of the mesmerizer conduct the mind and body through all the stages of sleep - from lassitude to slumber, and from slumber to a death-like trance, when, answering to no ordinary stimuli, the senses are apparently obliterated, the functions of intellectual existence sealed up, while only those of organic life remain, and the subject to all appearance but one remove from death itself. This is emphatically a state of sound sleep. Are the mental faculties during this inexplicable condition dormant? Speak to the subject, no reply is elicited: apply the knife to the dermoid texture, no sensation is acknowledged: present to the eye an illuminated body, no influence is excited. The natural avenues to the mind are closed, and it is unapproachable through ordinary means.

The power to set aside this mysterious condition lies with the agency that produced it, and through its influence, to reveal a mental state during sleep, which, without its assistance, must have remained among the things unknown.

The magnetizer, in operating upon the mental state of his subject, fixes his own mind intensely on some object with which the magnetized is unacquainted, and makes inquiries relative to it. He receives for answer a true description. This is probably a reflection of his own mind. But he does not always receive a correct reply. This may be owing to an imperfection in the mind of the magnetized, who may not be able to comprehend the subject; and because there is probably no power of creation; but only of eliciting what already exists. The questions are not invariably replied to, and reasons are sometimes assigned for withholding replies. This; is not a reflection of the mind of the manipulist, but a distinct act of volition, involving the reflective faculties. It is antagonistic to, and not in harmony with the will of the mesmerizer. The manipulist possesses the power of directing the mind of the magnetized to a particular subject, but without the power of controlling its operations. It is apparently dependent as to the selection of a subject for consideration; but afterwards acts upon it independently. In such case the individual presents his own mental characteristics. Should discretion be the prominent feature of his mind, his answers will be in harmony with sound sense; but if he is gifted with strong powers of imagination, his replies will partake largely of his own fanciful creations. The magnetizer appears to hold the same controlling influences through his mysterious communications, that surrounding objects do through the special senses, - the regulating power of the mind; but the result of the mental operations as manifested through the will is independent.

One of Dr. Elliotson's cases illustrates this mental independence of the magnetic state very explicitly. In the Doctor's solicitations for a song, his subject exhibited great impatience at his importunity, but upon his earnest request "she at length complied, and sang a ballad in a rather sweet voice, breaking off, however, in the middle with an impatient expression, "How tiresome you are! There, I forget it." "After some minutes, she resumed, and finished the song."

Dr. George Moore, in his "Body and Mind," relates the case of a boy with a headless supplemental trunk growing from the abdomen, which on being touched the sensation was acknowledged by, or in other words, referred to the corresponding part of the perfect body. In this ease it appears that the percipient principle of. one mind, acted for the sensations of another body. There are numerous cases of mesmeric record, where a like mental phenomenon is exemplified in separate bodies. For instance, when the sense of taste is intensely excited by highly flavored substances placed on the tongue of the mesmerizer, the same impression is perceived by the mesmerized, and so of the impressions of all the other senses. The books on mesmerism abound in examples of this kind.

Not long since we attended an exhibition of animal magnetism, and were appointed one of a committee to prevent or discover collusion between the parties, and we must frankly acknowledge that nothing of the kind could be detected; in fact, we were perfectly convinced that there was no attempt made at deception. At this exhibition there were two subjects - a young man about eighteen, and a young woman about twenty years of age. These subjects were thrown into the' mesmeric sleep at the same time, and retained under its influence for about three hours. In these cases, the mental faculties, so far as the subject of thought was concerned, were under the control of the mesmerizer, but the precise mode of mental manifestation was independent of him. In their answers to interrogatories, either written or verbal, they both replied at the same time in phraseology differing entirely, but expressing the same ideas. The locomotive power of one was subject to his will; and in her case, the voluntary muscular organs could be relieved of their rigidity by degrees. The arms would be perfectly rigid after the mind was restored to external relation, and the hands would remain* clenched while the flexor muscles of the arm and fore-arm were perfectly relaxed; a condition which our present knowledge of physiology does not account for, but which could be tested by the senses of touch and sight, beyond the possibility of deception. Was there not a faculty here developed, resembling that located in the claws of birds which sleep roosting, and which some suppose to be independent of the will, when the animal has taken its position for the night? These cases also exhibited the phreno-magnetic phenomena in an extraordinary degree. The application of the finger to an organ of one subject would instantly be manifested by the acts of the other sometimes in vocal expressions, and at other times in change of posture, understood as the phrenological language of attitude.