The Same, Questions, Book XXV. Gaius Seius, who was in the habit of transacting public business, lent money belonging to the Government at the ordinary rate of interest, but the custom existed to exact a higher rate where the interest was not paid within a certain time. Some of the debtors were in default in paying their interest, others paid more than they owed, and the result was that everything due by way of interest was made up, even that of those who had failed to pay anything. The question arose whether the surplus interest which was collected from some of the debtors, by way of penalty, according to the prevalent custom, should profit Seius himself, or should enure to the benefit of the Government? I answered that if Gaius Seius stipulated for interest from the debtors, that alone must be paid to the Government which, according to the rule, it was customary to collect from them, even though all the claims were good. 1Ad Dig. 22,1,11,1Windscheid: Lehrbuch des Pandektenrechts, 7. Aufl. 1891, Bd. II, § 439, Note 7.What if a public slave should have obtained an obligation bearing interest for the benefit of the Government? It is just that, although by law this interest should be due to the Government, still, on account of certain claims which are bad, a set-off of the surplus interest should be made, if the Government was not prepared to seize the property of all the debtors. Marcellus states almost the same opinion with reference to guardians.

Paulus, Questions, Book XXV. A broker who lent money at maritime interest, received certain merchandise which was in the ship by way of pledge, under the condition that if this was not sufficient to discharge the entire debt, he could have recourse to other merchandise loaded in different vessels, and which had already been pledged to other brokers with the understanding that if anything remained after they were satisfied, it would be considered pledged to the first broker. The question arose, if the first ship which contained sufficient merchandise to pay the entire debt should be lost, whether the loss should be borne by the creditor if the ship was destroyed within the days appointed to make the voyage; or whether he would still have a claim upon the merchandise which remained in the other ships. I answered that in other cases the diminution of the property pledged is at the risk of the debtor, and does not concern the creditor, but when money to be transported is paid on such a condition that the creditor will have no claim unless the vessel arrives safely at its destination within the specified time, the obligation of the loan itself, where the condition is not fulfilled, is held to be at an end; and therefore the right of the creditor to even those pledges which were not lost will be extinguished. If the ship should be lost within the specified time, and the condition of the stipulation is held not to have taken place, no question can then be raised with reference to the availability of the pledges which were in the other vessels. But when can the creditor claim possession of the other pledges? He will certainly be able to do so when the condition of the obligation is fulfilled; or the pledges which he first received have been lost by some accident, or sold at too low a price; or if the vessel should be lost after the time has passed during which he was bound to assume the risk.