The other example in the text seems still less relevant. Fear tends to accelerate the peristaltic motion, therefore there is a connection between certain states of the intestines and terrible ideas. To make this available for the author's purpose, the consequence of the connection ought to be, that acceleration of the peristaltic motion excites ideas of terror. But does it? The state of indigestion characteristic of hypochondria is not looseness of the bowels, but is commonly attended with the exact opposite. The author's usual acuteness of discernment seems to have been, in these cases, blunted by an unwillingness to admit the possibility that ideas as well as sensations may be directly affected by material conditions. But if, as he admits, ideas have a direct action on our bodily organs, a _prima facie_ case is made out for the localization of our ideas, equally with our sensations, in some part of our bodily system; and there is at least no antecedent presumption against the supposition that the action may be reciprocal--that as ideas sometimes derange the organic functions, so derangements of organic functions may sometimes modify the trains of our ideas by their own physical action on the brain and nerves, and not through the associations connected with the sensations they excite.--_Ed._]
{ 103} In illustration of the fact, that sensations and ideas, which are essential to some of the most important { 104} operations of our minds, serve only as antecedents to more important consequents, and are themselves so { 105} habitually overlooked, that their existence is unknown, we may recur to the remarkable case which we have just explained, of the ideas introduced by the sensations of sight. The minute gradations of colour, which accompany varieties of extension, figure, and distance, are insignificant. The figure, the size, the distance, themselves, on the other hand, are matters of the greatest importance. The first having introduced the last, their work is done. The consequents remain the sole objects of attention, the antecedents are forgotten; in the present instance, not completely; in other instances, so completely, that they cannot be recognised.[33] [34]
[Bain's footnote 33: Perhaps the most remarkable case of sensations overlooked on their own account, and considered only as a means of suggesting something else, is the visual, or retinal, magnitude of objects seen by the eye. This is probably the most delicate sensibility within the compass of the mind; and yet we habitually disregard it for all things near us, and use it solely for perceiving real magnitude as estimated by our locomotive and other members. The visual magnitude of a table, or other article in a room, is never thought of for itself; although incessantly fluctuating we never think of the fluctuations; we pass from these to the one constant perception, named the true or real magnitude. It is only for remote objects, as the sun and moon, the clouds, the distant hills, that the retinal magnitude abides with us in its own proper character. In looking down a vista, we may also be aroused to the feeling of retinal magnitude. For perspective drawing, it is necessary that we should arrest the strong tendency to pass from the visible, to the real, forms and dimensions of things.--_B._]