Note 21 — Chapter II · THE SMILE AND THE LAUGH.
Reading edition
Angell and Thompson in the article quoted above suppose that the whole dilation of the capillaries during laughter is a secondary effect of sudden changes in the breathing. This seems a reasonable conclusion. Yet since, according to these writers, smiling as well as mild laughter causes gentle changes of the same kind, it seems possible that we have here, in a disguised form, the working of the general law stated by these writers: that agreeable experiences are accompanied by dilation of the peripheral blood-vessels.