With these general considerations to help us, we may now look at the course of development of the laughing experience during the first three years. It may be premised that the smile and the laugh only become gradually differentiated as signs of qualitatively dissimilar attitudes. In the case of Ruth the two expressions remained for a time interchangeable, and frequently {194} alternated in the same fit of joyous delight. But about the 129th day the smile, it is remarked, began to take on one of its specialised functions, the social one of greeting. Coming now to laughter, we have found that it begins at an early date to pass from a general sign of sudden increase of pleasure or good spirits into something akin to mirthful play. This has been illustrated in the early responses to tickling, and, a little later, to simple forms of a laughing game (_e.g._, bo-peep). By what process of change, one may ask, does the impulse to laugh when the heart suddenly grows glad pass into the laughter of play? Allowing, as seems certain, that the play-impulse is inherited, can we point out any psychological connection between the two? The answer has already been given in substance in our general analysis of the causes of laughter. A sudden rise of pleasurable consciousness, when it possesses the mind and becomes gladness, say the infant’s flood of delight at the swinging coloured baubles, necessarily dissolves, for the time, the tense, serious attitude into a loose, play-like one. The child’s consciousness is now all gladness in face of his bauble; and play is just another way of effecting this dissolution of the serious attitude into a large gladness. Not only so, but the elemental mood of laughter resembles the play-mood, since it finds its satisfaction in pretence or make-believe. The gladdening object divested of all serious interest becomes a play-thing, a mere semblance of the thing of practical account which the child observed in the serious moments. Its greeting by the senses may be described, indeed, as a kind of play of these senses. Hence, the specialisation of the primal laughter of delight into that of fun would appear to be one of the simplest processes in the whole development of the emotion. {195} We may now briefly trace out some of the phases of development of these two primal forms of laughter.