This chapter is an elaborate statement of the subject as well as the object of the inquiry. The term ψυχή, here rendered "Vital Principle," has several significations, as was observed in the preface, in the course of this and the other physiological treatises: in one passage, it implies the life of an animal; in another, the nutritive function ; in another, a vital part; in another, a motor force; and in another, the visual power (τοῦ ὄμματος ἡ ψυχή[1]); some writers, besides, derived the term ψυχή from ψυχρὸς or ψυχός, coolness or cold, because respiration was held to be a cooling process, and as such essential to life. The object of Aristotle, then, in this treatise, was to learn the nature of that essence or principle which, under whatever denomination, is the innate source of motion, and, consequently, of vital actions in all bodies capable of being animated; for although, in the more complicated forms of being, it is involved in the manifestation of perceptions and passions, its great office still is to originate, to maintain, and to perpetuate life, through all its gradations. It may be that, from some such conclusion, Aristotle was led to regard the vital principle as inferior in destiny and office to the faculty which he has designated[2] mind (ὁ νοῦς), and made to be impassive, homogeneous, apart from, and independent of, the body. These opinions have much in common with those adopted by Plato in the Timæus; as, while, in that most beautiful and intellectual disquisition, the senses, appetites, and passions, the mortal framework, that is, of the sentient being, are located about the heart and liver,—the intellectual faculty, that which is divine, and intended to direct and control the animal powers, is placed in the head. The life is represented, in fact, by ψυχή, which is bound up with corporeal functions and appetites; and reason by νοῦς, which, if any where, is, "as the divine seed of wisdom," in the brain; and, being homogeneous, does not depend, for existence, upon the life of the body. These few words will suffice to shew that there is an analogy between the two systems of physiology and psychology.