Oh dear, oh dear. I think this is incomprehensible without some context. The learned judge appears to be quoting here from the Digests of Justinian 46.3.1. At this point the Digests are citing a jurist named Domitius Ulpianus, who died in 223 AD, and who, in the text cited, was in turn was commenting on a first-century jurist named Sabinus:
Ulpianus 43 ad sab.
Quotiens quis debitor ex pluribus causis unum debitum solvit, est in arbitrio solventis dicere, quod potius debitum voluerit solutum, et quod dixerit, id erit solutum: possumus enim certam legem dicere ei quod solvimus. quotiens vero non dicimus, in quod solutum sit, in arbitrio est accipientis, cui potius debito acceptum ferat, dummodo in id constituat solutum, in quod ipse, si deberet, esset soluturus quoque debito se exoneraturus esset, si deberet, id est in id debitum, quod non est in controversia, aut in illud, quod pro alio quis fideiusserat, aut cuius dies nondum venerat: aequissimum enim visum est creditorem ita agere rem debitoris, ut suam ageret. permittitur ergo creditor constituere, in quod velit solutum, dummodo sic constituamus, ut in re sua constitueret, sed constituere in re praesenti, hoc est statim atque solutum est...
Now this is difficult, somewhat technical Latin—at least I find it so. I did attempt a translation of my own, and got the gist of it. But the “gold standard†of this in English is the version of one Samuel Smith:
Ulpianus, On Sabinus, Book XLIII.
Whenever a debtor, who owes several debts, pays one of them, he has the right to state which obligation he prefers to discharge, and the one which he selects shall be paid, for we can establish a certain rule with reference to what we pay. When, however, we do not indicate which debt is paid, he who receives the money has the right to say on what claim he will credit it, provided he decides that it shall be credited on a debt which, if he himself owed it, he would have paid, and be discharged from liability, where he actually owed it, that is to say a'n obligation which is not in dispute; or one for which no surety has been given, or which has not yet matured; for it appears perfectly just for the creditor to treat the property of the debtor as he would treat his own. Therefore, the creditor is permitted to select the debt which he desires to be paid, provided that he makes his selection as he would do with reference to his own property; he must, however, decide immediately, that is, as soon as payment is made...
I have no idea why there’s an apostrophe in that “an†but I’ve checked two different texts, and it's there in both of them.
I have put your words, and Smith's version of them, in boldface.
Does this answer your question? I would be curious to know how all this applies to your ninteenth-century case.