from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
EXTINCTION OF A THING. When a thing which is the subject of a contract has
been destroyed, the contract is of course rescinded as, for example, if Paul
sell his horse Napoleon to Peter, and promises to deliver him to the buyer
in ten days, and in the mean time the horse dies, the contract is rescinded,
as it is impossible to deliver a thing which is not in esse; but if Paul
engage to deliver a horse to Peter in ten days, and, for the purpose of
fulfilling his contract, he buys a horse and it die, this is no cause for
rescinding the contract, because he can buy another and complete it
afterwards. When the subject of the contract is an individual, and not
generally one of a species, the contract may be rescinded; when it is one of
a species which has been destroyed, then, it may still be completed, and it
will be enforced. Lec. El. Dr. Rom. Sec. 1009.