Old-fashioned, laughter at the, [281].

Optimism and pessimism. See also Philosophy, Worth of Life.

Order, breach of, as laughable, [94], [266], [342].

Organism, effects of laughter on, [33]–36, [45], [69]; resonance of, as factor in laughter, [44], [47].

Origin of laughter, [155] (Chapter VI.); first appearance in child, [166], [170]; early laughter as expression of pleasure, [169]; an inherited tendency, [170]; first appearance in primitive man, [173]; development out of smile, [173]–176; explosive vigour, explanation of, [176]. See also Smile, Tickling.

Paradox, as laughable, [104], [106], [110].

Parasites, laughter of tickling as defensive against, [178], [179], [181].

Parnell, J., [111] note.

Pascal, B., [1], [423].

Peacock, T. L., [222].