Agency- gratuitous agent- duty of care- gratuitous agent undertaking
work without requisite skill only liable for failure to exercise reasonable
care of ordinarily prudent man: Where a person, not professing to be
skilled in the particular matter, undertakes to do an act for another,
without reward, he is only bound to exercise that care which he, as an
ordinarily prudent man, would exercise if acting for himself; so that
where a person who is not specifically trained for the job attempts,
without reward, to float a submerged motor launch and tow her to safety
and fails to exercise reasonable care in so doing, he is guilty of negligence
only in so far as he has not exercised the degree of care which would
have been exercised by an ordinarily prudent man.