[1] I would mention that in the progress of my discoveries, especially in 1838-39, I came into frequent and intimate association with the late Prof. Wm. Byrd Powell, M. D., the most brilliant, and original of all American students of the brain, whose lectures always excited a profound interest in his hearers, and, in comparing notes with him, I found my own original observations well sustained by his. Though erratic in some of his theories, he was a bold student of nature, and the accidental destruction of his manuscript by fire, when too late in his life to repair the loss, was a destruction of much that would have been deeply interesting. It was absolutely necessary that the functions of the brain should be demonstrated as positively as those of the spinal nerves had been demonstrated by Majendie and Bell. Two methods appeared possible. The two agents were galvanism and the aura of the nervous system, commonly called animal magnetism. My first experiments in 1841, satisfied me that both were available, but that the _nervaura_ was far more available, efficient, and satisfactory. Upon this I have relied ever since, though I sometimes experiment with galvanism, to demonstrate its efficiency, and Dr. De la Rua, of Cuba, informed me over twenty years ago that he found very delicate galvanic currents available for this purpose in his practice. Animal magnetism or mesmerism had been involved in mystery and empiricism. There had never been any scientific or anatomical explanation of the phenomena, and this mystery I desired to dispel. My first step was to ascertain that for experiments on the nervous system we did not need the somnambulic or hypnotic condition, and that it was especially to be avoided as a source of confusion and error. Whenever the organ of sensibility, or sensitiveness, was sufficiently developed and predominant, the conditions of neurological experiments for scientific purposes were satisfactory, and to make such experiments, the subjects, instead of being ignorant, passive, emotional, hysteric, or inclined to trance, should be as intelligent as possible, well-balanced and clear-headed,--competent to observe subjective phenomena in a critical manner. Hence, my experiments, which have been made upon all sorts of persons, were most decisive and satisfactory to myself when made upon well-educated physicians, upon medical professors, my learned colleagues, upon eminent lawyers or divines, upon strong-minded farmers or hunters, entirely unacquainted with such subjects, and incapable of psychological delusion, or upon persons of very skeptical minds who would not admit anything until the phenomena were made very plain and unquestionable.