When a thing which is the subject of a contract has been destroyed, the contract is of course rescinded as, for example, if Paul sell his horse Napoleon to Peter, and promises to deliver him to the buyer in ten days, and in the mean time the horse dies, the contract is rescinded, as it is impossible to deliver a thing which is not in esse; but if Paul engage to deliver a horse to Peter in ten days, and, for the purpose of fulfilling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 When the subject of the contract is an individual, and not generally one of a species, the contract may be rescinded; when it is one of a species which has been destroyed, then, it may still be completed, and it will be enforced.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. Section 1009.