Adopting this hypothesis, we should expect that the differences in the composition of the sensations already dealt with would lead to the result that, whereas some are preponderantly agreeable, others are rather disagreeable. And this, I believe, accords with the results of observation. The tickling sensations excited by stimulating the hairy orifices of the ear and the nostril are said by Dr. Louis Robinson to be “distinctly distasteful”. The sensations produced by tickling the sole of the foot are commonly held, at least by older children and adults, to be disagreeable in all degrees of their intensity. This certainly accords with my own self-observation. The lightest touch, say from a shampooer’s hand, is to me distinctly “nasty,” with an uncanny nastiness which I cannot hope to describe. An example of a distinctly agreeable sensation of tickling is, curiously enough, supplied by another hairless surface, closely analogous to the sole, namely the palm. A lady, who is an excellent observer of children and endowed with an exceptional memory of her early experiences, tells me that when a child she loved to have her hands tickled. Her feeling was a kind of “awful joy,” the awfulness coming {56} from a vague suspicion that the pastime was not quite proper. Other preponderantly agreeable varieties appear to be the sensations produced by the lighter stimulation of those parts which seem in a special way to be laughter-provoking areas, _e.g._, the armpits and ribs. This is, at least, suggested by the fact that younger children love to be tickled in these parts in moderation, and will ask to have the pastime renewed. An important characteristic of these feeling-tones is their unsteadiness or changefulness. Although at a particular moment we may be able to detect clearly a slight preponderance of the agreeable or of the disagreeable aspect, it is only for a moment. An increase in the degree of pressure, a further prolongation of the stimulation, or even a slight variation in the mode of contact, may suffice to bring up and render prominent the opposed feeling-phase. We may now pass to the motor reactions, which are of more especial interest in the present connection. Overlooking the less conspicuous elements, such as the contraction of the muscles of the hairs, we find that there are two easily distinguishable groups of movements: (_a_) a number of protective or _defensive_ reactions which are adapted to warding off or escaping from the attack of the tickling stimulus; (_b_) movements expressive of pleasure and rollicking enjoyment, from the smile up to uproarious and prolonged laughter.