Life and mind, in their abstract nature or essence alike inscrutable to us, are problems which belong to the same category; for, in this world, we know nothing of life apart from an organism, and we have no manifestations of mind independently of a brain and nervous system. Here living organisms are required for the display of the vital phenomena, and a brain and nervous system for the manifestations of mind. Life has accordingly been defined as “the collective expression for a series of phenomena which take place exclusively in bodies that are organized,” and “mind as the functional manifestations of the living brain.” But then, and at the outset, it is to be remembered that in affirming sensation, emotion, thought, and volition to be functions of the nervous system, what is really maintained is this, that the vesicular matter of the encephalic ganglia furnishes the material conditions—the medium through which these mental phenomena are made manifest in this life. It may indeed be asked, Are not the physical forces of external nature, which underlie all vital phenomena, and the changing states of consciousness which constitute our mental life, as inscrutable to us in their nature or essence as are life and mind ? and it must be conceded that they are. Matter and force are coexistent, and are correlative. Nor can we conceive of the one but in association with, by, and through the other, any more than we can conceive of life, in our present state of existence, apart from an organism, or of thought independently of a living brain.