When he left more than three descendants, she was entitled to participate with them equally. If there were only three or fewer, she was entitled to one fourth of the estate. If she had children by the deceased, she had only the usufruct of her portion during her life, and was bound to preserve it for them. If a man had no legitimate children, he could leave his whole inheritance to his natural children, or to their mother; but if he had lawful children, he could leave only one twelfth to the natural children and their mother. If the father died intestate, without leaving a lawful wife or issue, his natural children and their mother were entitled to one sixth of the succession, and the rest was divided among the lawful heirs. [Sidenote: Contracts.] In the matter of contracts, the Roman law was especially comprehensive, and the laws of France and Scotland are substantially based upon the Roman system. The Institutes of Gaius and Justinian distinguish four sorts of obligation,--aut _re_, aut _verbis_, aut _literis_, aut _consenser_. Gibbon, in his learned chapter, prefers to consider the specific obligations of men to each other under promises, benefits, and injuries. Lord Mackenzie treats the subject in the order of the Institutes. "Obligations contracted _re_--by the intervention of things--are called by the moderns real contracts, because they are not perfected till something has passed from one party to another. Of this description are the contracts of loan, deposit, and pledge. Till the subject is actually lent, deposited, or pledged, it does not form the special contract of loan, deposit, or pledge." [Footnote: Mackenzie.] [Sidenote: Loans.]