Nothing, which is not intented to cause death, is an offence by reason of
any harm which it may cause, or be intended by the doer to cause, or be
known by the doer to be likely to cause, to any person for whose benefit it
is done in good faith, and who has given a consent, whether express or
implied, to suffer that harm, or to take the risk of that harm.
A, a surgeon, knowing that a particular operation is likely to cause the death of Z, who suffers under the painful complaint, but not intending to cause Z's death, and intending, in good faith, Z's benefit, performs that operation on Z, with Z's consent. A has committed no offence.