Laughing is not always the proof of a mind at ease. – Proverb

A good, real, unrestrained, hearty laugh is a sort of glorified internal massage, performed rapidly and automatically. It manipulates and revitalizes corners and unexplored crannies of the system that are unresponsive to most other exercise methods. – Author unknown, from an editorial in New-York Tribune, quoted in Quotations for

No man who has once heartily and wholly laughed can be altogether irreclaimably bad. – Thomas Carlyle, Sartor Resartus