14 Contrariwise, if a debtor leaves his creditor a legacy of what he owes him, the legacy is void, if it includes no more than the debt, for the creditor is thus in no way benefited; but if the debtor unconditionally bequeaths a sum of money which the creditor cannot claim until a definite date has arrived or a condition has been satisfied, the legacy is good, because it confers on the creditor a right to earlier payment. And, even if the day arrives, or the condition is satisfied, during the testator's lifetime, Papinian decides, and rightly, that the legacy is nevertheless a good one, because it was good when first written; for the opinion that a legacy becomes void, because something happens to deprive it of all material effect, is now rejected. 15 If a man leaves his wife a legacy of her dowry, the gift is good, because the legacy is worth more than a mere right of action for the dowry. If, however, he has never received the dowry which he bequeaths, the Emperors Severus and Antoninus have decided by rescript that the legacy is void, provided the general term 'dowry' is used, but good, if in giving it to the wife a definite sum or thing is specified, or described generally by reference to the dowry deed. 16 If a thing bequeathed perishes through no act of the heir, the loss falls on the legatee: thus if a slave belonging to another person, who is given in this way, is manumitted through no act of the heir, the latter is not bound. If, however, the slave belongs to the heir, who manumits him, Julian says that he is bound, and it is immaterial whether he knew or not that the slave had been bequeathed away from him. 17 If a testator gives a legacy of female slaves along with their offspring, the legatee can claim the latter even if the mothers are dead, and so again if a legacy is given of ordinary slaves along with their vicarii or subordinates, the latter can be claimed even if the former are dead. But if the legacy be of a slave along with his peculium, and the slave is dead, or has been manumitted or alienated, the legacy of the peculium is extinguished; and similarly, if the legacy be of land with everything upon it, or with all its instruments of tillage, by the alienation of the land the legacy of the instruments of tillage is extinguished. 18 If a flock be given as a legacy, which is subsequently reduced to a single sheep, this single survivor can be claimed; and Julian says that in a legacy of a flock are comprised sheep which are added to it after the making of the will, a flock being but one aggregate composed of distinct members, just as a house is but one aggregate composed of distinct stones built together. So if the legacy consists of a house, we hold that pillars or marbles added to it after the making of the will pass under the bequest.