delivered the opinion of the court.

The question did not arise whether the custom which the plaintiff offered to prove could have been proved as the measure of his compensation, in the absence of any express contract, because the plaintiff had introduced in evidence a letter from the defendant in reference to this compensation, under which he said he had acted in taking the policies for which he now claimed the additional commission. There was no question as to the amount, or percentage, or premium, which was to be paid under this letter. The plaintiff stated that he had retained a certain percentage, which \w.as that allowed by the company. The testimony' was not *579offered to show what was the highest commission paid by the company.

It appears to us, as it did to the Circuit Court, that the testimony offered would have established a new and distinct term to the contract. It would have established a contract very different from the written one introduced by plaintiff. The language of the letter was neither ambiguous nor technical. It required and needed no expert, no usage to discover its meaning. To have admitted the usage offered in evidence in this case would have been to make a contract for the parties differing materially from the written one under which they had both acted for some time.

The tendency to establish local and limited usages and customs in the contracts of parties, who had no reference to them when the transactions took place, has gone quite as far as sound policy can justify. It places in the hands of corporations, such as hanks, insurance companies, and others, by compelling individuals to comply with rules established for the interests alone of the former, a power of establishing those rules as usage or custom with the force of law. When this is confined to establishing an implied contract, and the knowledge of'the usage is brought home to the other party, the evil is not so great. But when it is sought to extend the doctrine beyond this, and incorporate the custom into an express contract whose terms are reduced to writing and are expressed in language neither technical nor ambiguous, and therefore needing no such aid in its construction, it amounts to establishing the principle that a custom may add to or vary or contradict the well-expressed intention of the parties made in writing. No such extension of the doctrine is consistent either with authority or with the principles which govern the Jaw of contracts.

A question is raised in this court not raised in the Circuit Court as to the right of the defendant to recover, by way of set-off or cross-action against the plaintiff’, a 6um of money in his hands as agent of the plaintiff, which was admitted to be due, if plaintiff’s claim was not established. The amount was admitted by plaintiff, and no objection was *580made to pleading it as a set-off. Therefore, none can be made here. But if the point were open to inquiry, it is settled by the case of West v. Aurora City,* that defendants in the Circuit Courts of the United States can avail themselves of the laws which prevail in the State concerning the right of set-off generally. It would be a most pernicious doctrine to allow a citizen of a distant State to institute in these courts a suit against a citizen of the State where the court is held and escape the liability which the laws of the State have attached to all plaintiffs of allowing just and legal set-offs and counter claims to be interposed and tried in the same suit and in the same form.

Judgment affirmed.