It is apparently that sensation in which the actual contact of the psyche with the material occurs--an immediate sensation of the nature of matter--namely, the =sense of smell=. The metaphysical significance of the sense of smell has been aptly indicated by describing that sense as the “sublimated thing-in-itself,” as a sense which, like no other sense, allows us to enter immediately into the nature of matter; it is, in fact, the sense of personality. “Smell,” says Heinrich Steffens, “is the principal sense of the higher animals; it represents for them their own inner world; it envelops their existence. Upon smell, wherein sympathy and antipathy are represented, is based the whole security of the higher animal instinct; =for carnal desire is comprehended in this sense=.... Indeed, in sexual union the subjective sensation which is developed by means of smell blends completely with the objective, and from the monistic union of the two arises the intenser libido, wherein the unfathomableness of the procreative force and the whole power of sex are absorbed.” Ernst Haeckel ascribes to the two sexual cells a kind of inferior psychical activity; he believes that they experience a sensation of one another’s proximity; and indeed it is probably a form of sensory activity analogous to the sense of smell that draws them together. The sensation of the two sexual cells, which Haeckel believes to be situated especially in the cell nuclei, he denotes by the term “erotic chemotropism.” He attributes it to an attraction of the nature of smell, and considers that it represents the psychical quintessence, the original being of love. A later investigator, Eugen Kröner, holds the same view. In the conjugation of two vorticellæ he recognizes the influence of the chemically operative sensation of smell; to him smell is the most important element in the sexual impulse of animals.