The description of laughter here offered applies only to the typical form. It would have to be modified considerably to suit the attenuated forms to which the expression is reduced in “polite society”. Of these, more presently. Even where the vocal outburst retains its primitive spontaneity and fulness considerable variations are observable, connected with differences in the whole respiratory and vocal apparatus. The intensity and volume of the sound, the pitch and vowel-quality, the rapidity of the successive expirations, the length of the series, the mode of commencing and of ending, may all exhibit variations which help to make the laughter of one person or of one race different from that of another. We may now pass to some other accompaniments of the muscular movements of laughter. It is of importance to study these with care if we wish to estimate the precise value of the hilarious explosion in the economy of human life. {33} Since the movements of laughter are sudden and violent interruptions of the smooth rhythmic flow of the respiratory process, we may expect to find that they have important organic effects, involving not merely the mechanism of respiration, but also that of the circulation of the blood. Here, it seems, we have to do with a double effect First of all (we are told), this series of spasmodic expirations—during which, as we have seen, the glottis is partially closed—increases the pressure within the thorax or chest, and so impedes the entry of blood from the veins into the heart. This effect is seen in the turgidity of the head and neck which appears after prolonged and violent laughing. In the second place, the exceptionally deep inspirations tend to expand the lungs with air, and to drain off the blood from the veins into the heart. The manner in which these two actions, the deepened inspiration and the prolonged expiration, alternate during a fit of laughter, appears to secure a considerable advantage in respect both of accelerated circulation and more complete oxygenation of the blood. The brisker movement of the blood after laughter has recently been observed in some experimental inquiries into the effects of emotional excitement of various kinds on the pulse.[17] It is not improbable that this expedited circulation produces more remote effects on the organism. It has been suggested that one of the advantages of a “good laugh” is that it relieves the brain, and this would seem to imply that it quickens the movement of the blood through the fine and readily clogged vessels which permeate the brain-structures. {34}