7 A mother or maternal grandfather is not bound to institute her or his children or grandchildren; they may simply omit them, for silence on the part of a mother, or of a maternal grandfather or other ascendant, has the same effect as actual disinherison by a father. For neither by the civil law, nor by that part of the praetor's edict in which he promises children who are passed over possession of goods against the will, is a mother obliged to disinherit her son or daughter if she does not institute them heirs, or a maternal grandfather to be equally precise with reference to grandchildren by a daughter: though such children and grandchildren, if omitted, have another remedy, which will shortly be explained. TITLE XIV. OF THE INSTITUTION OF THE HEIR A man may institute as his heirs either free men or slaves, and either his own slaves or those of another man. If he wished to institute his own slave it was formerly necessary, according to the more common opinion, that he should expressly give him his liberty in the will: but now it is lawful, by our constitution, to institute one's own slave without this express manumission--a change not due to any spirit of innovation, but to a sense of equity, and one whose principle was approved by Atilicinus, as it is stated by Seius in his books on Masurius Sabinus and on Plautius. Among a testator's own slaves is to be reckoned one of whom he is bare owner, the usufruct being vested in some other person. There is, however, one case in which the institution of a slave by his mistress is void, even though freedom be given him in the will, as is provided by a constitution of the Emperors Severus and Antoninus in these terms: 'Reason demands that no slave, accused of criminal intercourse with his mistress, shall be capable of being manumitted, before his sentence is pronounced, by the will of the woman who is accused of participating in his guilt: accordingly if he be instituted heir by that mistress, the institution is void.' Among 'other persons' slaves' is reckoned one in whom the testator has a usufruct.