If (2) we now turn to the converse case, the qualification of actual touch experience by revived visual experience, we find the union of the constituents of the complex much looser. This does not mean that they are more easily separable; for the association in normal human experience is almost, if not quite, indissoluble. But when the tactual experience is primary, the reinstated visual experience is much more prominent, more readily distinguishable and separately appreciable, than is the reproduced tactual element when the visual experience is primary. "We have here a case of complication which approaches most closely to free reproduction. When we close our eyes and touch an object, we need not indeed have a distinct picture of the surface touched. But the slightest reflective scrutiny is enough to show that the total impression is complex, containing a visual as well as a tactual constituent, and also, in most cases, that the visual constituent is as prominent as the tactual or even more so.

(b) Free Reproduction.—In free reproduction, the reproduced mode of consciousness, b, is capable of existing apart from the A which reinstates it. b has an individuality of its own distinct from A, and it can therefore follow A in time, continuing to exist when A has disappeared. Trains of ideas supply by far the most familiar and important illustration. In complication, on the other hand, the existence of b is bound up with the existence of A. "To realise this difference,'' says Dr. Ward, "we need only to observe first how the sight of a suit of polished armour, for example, instantly reinstates and steadily maintains all that we retain of former sensations of its hardness and smoothness and coldness, and then to observe how this same sight gradually calls up ideas, now of tournaments, now of crusades, and so through all the changing imagery of romance."* The characteristics of ideas and the nature of their distinction from actual perceptions are topics which will be fully discussed at a later stage. It is sufficient to notice here (1) that any reproduction which can be called an idea, must have sufficient independence to be capable of forming a distinct link in a train of thought; (2) that it must be the thought of an object, such as a thing, quality, relation, or event, and not a mere crude sensation, however faint; (3) that just because an idea differs from an actual perception, ideal reproduction+ is always of a partial and modified character. The mental image of the flower, as called up by the name, is a typical illustration (cf., § 7 Association and Reproduction).

Ibid.            + Reproduction which takes the form of an idea.

Is free revival in every case ideal revival, or does it also take other forms? In particular, are sensations, as such, ever reinstated? Can they be recalled in their original sensational character without recurrence of the appropriate external stimulus? This is an important question. Broadly speaking, we may affirm that the direct reproduction of sensations, as such,*" is an exceptional and abnormal event. But there is an indirect process by which sensations of a certain class may be reexcited, although some of the conditions determining their first occurrence are by no means operative. Some sensations belong to the class called organic. It is characteristic of these that they are immediately excited, not by impressions upon the external organs of sense, but by the changing states of the internal organs, such as muscles, glands, and the like. Now, change in the state of these internal organs is, in a very important measure, determined from within the body by changing conditions of the nervous system. Any strong nervous disturbance tends to discharge itself over the whole organism, affecting respiration, heartbeat, tension of the muscles, circulation of the blood, secretion, etc. Such a nervous disturbance may, in the first instance, bo set up by an external impression such as a wound or a blow. But it may be afterwards more or less reproduced by association without the external impression, and it may then internally generate organic sensations bearing a marked similarity to those which accompanied its original occurrence. These sensations may without impropriety bo said to be reproduced, though in a circuitous manner. The physiological stimulus is indirectly reinstated, and it directly produces the sensation. Tickling is not merely a skinsensation. The skinsensation sets up changes in the central nervous system which determine diffused organic disturbance, including spasmodic movements, and the resulting organic sensation constitutes what is most specific in the experience of being tickled. But a similar effect may be induced without actual contact. By merely making" believe to tickle a sensitive person it is possible to produce the nervous disturbance with the resulting organic sensations and convulsive movements. In like manner, the mere sight of nauseous food may produce nausea and even vomiting. The intense organic discomfort which may be occasioned by merely looking on at a surgical operation, or even by seeing surgical instruments, has the same origin.

* By sensation, as such, is meant sensation with the peculiar intensely and liveliness which it possesses when produced by an external stimulus acting on a senseorgan.