[10] Such verbal suggestion, moreover, acting through a sense-impression, has something of that vividness of effect which belongs to all excitation of mental images by external stimuli. [11] See Wundt, _Physiologische Psychologie_, p. 723. [12] For a confirmation of the view adopted in the text, see Professor Bain, _The Senses and the Intellect_, Part II. ch. i. sec. 8; Herbert Spencer, _Principles of Psychology_, vol. i. p. 234, _et passim_; Dr. Ferrier, _The Functions of the Brain_, p. 258, _et seq._; Professor Wundt, _op. cit._, pp. 644, 645; G. H. Lowes, _Problems of Life and Mind_, vol. v. p. 445, _et seq._ For an opposite view, see Dr. Carpenter, _Mental Physiology_, fourth edit., p. 220, etc.; Dr. Maudsley, _The Physiology of Mind_, ch. v. p. 259, etc. [13] See note, p. 22. [14] Touch gives much by way of interpretation only when an individual object, for example a man's hat, is recognized by aid of this sense alone, in which case the perception distinctly involves the reproduction of a complete visual percept. I may add that the organ of smell comes next to that of hearing, with respect both to the range and definiteness of its simultaneous sensations, and to the amount of information furnished by these. A rough sense of distance as well as of direction is clearly obtainable by means of this organ. There seems to me no reason why an animal endowed with fine olfactory sensibility, and capable of an analytic separation of sense elements, should not gain a rough perception of an external order much more complete than our auditory perception, which is necessarily so fragmentary. This supposition appears, indeed, to be the necessary complement to the idea first broached, so far as I am aware, by Professor Croom Robertson, that to such animals, visual perception consists in a reference to a system of muscular feelings defined and bounded by strong olfactory sensations, rather than by tactual sensations as in our case. [15] It may be said, perhaps, that the exceptional direction of attention, by giving an unusual intensity to the impression, causes us to exaggerate it just as in the case of a novel sensation. An effort of attention directed to any of our vague bodily sensations easily leads us to magnify its cause. A similar confusion may arise even in direct vision, when the objects are looked at in a dim light, through a want of proper accommodation. (See Sir D. Brewster, _op. cit._, letter i) [16] They might also be distinguished as objective and subjective illusions, or as illusions _a posteriori_ and illusions _a priori_.