This, in brief, is the conclusion to which the "scientific imagination" of the present day, extending as it does from the known into the unknown, is slowly but surely leading up. Taking as our postulate the scientific statement of the atomic structure of bodies, atomic vibration and molecular arrangement, we turn to consider the action exerted by such bodies upon the nervous organism of man. The function of the brain--which must be regarded as the bulbous root of a nervous plant whose branches grow downwards--is twofold; to affect, and to be affected. In its active or positive condition it affects the whole of the vital and muscular processes in the man, finding expression in vital action. In its passive or negative state it is affected by impressions coming to it in different ways through the sense-organs, resulting in nervous and mental action. It is this latter phase of brain-function with which we are immediately concerned. The range of our sense-perception puts us momentarily and continually in relation with the material world, or rather with a _certain portion_ of it. We say a certain portion because we know from scientific experience that the scale or gamut of sense-perception is limited, both as to its extent and as to its quality. Many insects, birds, and quadrupeds have keener perceptions in some respects than man. The photographic plate can register impressions which are beyond the perception of our highest sense of sight. The Roentgen rays have put us into relations with a new order of impression--records quite beyond the range of our normal vision. The animalcule and microbic life, itself microscopic, has yet its own order of sense-organs related to a world of vitality beyond our ken. These, and a host of other observations, serve to show that our normal perceptions are extremely limited, and, further, that nature does not cease to exist where we cease to perceive her.