Q.E.D.
PROP.XLI.

Pleasure in itself is not bad but good: contrariwise, pain in itself is bad.
Proof .-- Pleasure (III.xi.and note) is emotion, whereby the body's power of activity is increased or helped; pain is emotion, whereby the body's power of activity is diminished or checked; therefore (IV.

xxxviii.) pleasure in itself is good, &c.

Q.E.D.
PROP.XLII.

Mirth cannot be excessive, but is always good; contrariwise, Melancholy is always bad.
Proof .-- Mirth (see its Def.