delivered the opinion of this court:
This was an action of assumpsit, instituted by the appellee as the assignee of an account due to Messrs. Hodges and Brooke, for medical services rendered, and medicines furnished to David Crawford, the intestate. The appellant pleaded non assumpsit, and limitations, and upon those pleas issues were joined.
*217The assignment was as follows: — ■
“ In consideration of the natural love and affection we bear our several and respective children, we and each of us, do hereby grant, bargain, transfer, assign and set over, all our respective right, title, interest and claim, of, in, and to, the within account, to John B. Brooke, upon the following trust, to wit, that the proceeds of said account, when collected, after deducting the expenses thereof, shall be immediately applied, according to our respective interests therein; to the exclusive benefit and advantage of our several children, by the said John B. Brooke, trustee, as aforesaid.”
At the trial of the cause, the plaintiff below offered Henry Brooke, one of the assignors, as a witness, to prove the rendition of the services charged in the account, and an acknowledgment of, and promise to pay, the same, by the intestate, within three years before the institution of the suit.
The defendant objected to the competency of this witness, but the court overruled the objection; and the correctness of the opinion of the court on this question, forms the subject of the first exception.
The fact, that the witness offered by the plaintiff was one of the assignors, constituted in itself no objection to his competency, if he had parted with his whole interest in the claim, and could neither gain, nor lose, by the event of the suit. 'When objection is made to the competency of a witness, upon the ground of interest, the inquiry is not, whether he was originally interested; but, is he interested at the moment his testimony is tendered to the court ? And if it appears at the time he is presented to the court, he has no interest in the result of the controversy, the circumstance that he wa.s once the owner of the cause of action, and has assigned it, interposes no obstacle to his examination. This is clear upon principle, and has been directly decided. 9 Wend., 295. 3 Bin., 313. 1 Raw. 434.
In the case of Stimmel against Underwood, 3 G. & J., 287, the Court of Appeals have defined ihe kind of interest which will exclude a witness from testifying in a cause. They determine, that it must be a legal interest, and that a mere honorary obligation will not render him incompetent. This *218rule upon the subject of interest, remained unsettled until the decision of the court of King’s Bench, in Belt against Baker, 3 Term., 27; but it is now established, that the only cases, in which, for this cause, a witness is incompetent, are, where he has a legal, certain, and immediate, interest in the event of the suit itself; or in the record, as an instrument of evidence, in support of his own claims in a subsequent action. Doe vs. Tyler, 6 Bing., 390. 1 Greenl. Ev., 432. Applying this test to the competency of the witness, we can discover no reason for excluding him.
It is certainly true, that where the situation of the witness is such, that he would become responsible to the party by whom he is required to give testimony, for the expenses which might be incurred in the prosecution of a claim, in case of defeat, he is incompetent; for he has a direct interest in sustaining the cause of the party by whom he is called. 3 C. & Pai., 571. And if the counsel for the appellants could have maintained their proposition, that the assignor was responsible to the plaintiff below, for the expenses to which he might be subjected in a contest for this debt, they would have shown a case in which the witness was to be excluded. But such is not the predicament of the witness. The assignment provides, that the expenses are to be paid out of the fund, when collected; and on the contingency of the plaintiff failing in the action, and being, therefore, obliged to pay the costs of the suit, there could be deduced from this assignment, voluntary as it is in its character, no legal obligation express or implied, to indemnify the plaintiff for the expenses thus incurred by him. The fact, that the witness might consider the circumstances under which the assignment was made, as imposing upon his honor an obligation to protect his trustee from loss, is an objection which would go only to his credibility. We think, therefore, that the court below decided correctly, in permitting the witness to be examined.
The decision, however, of the court below, in the second exception, presents a very different question.
It is stated, that after the witness had been examined in chief, the defendant, for the purpose of showing that the *219account had not been bona fide assigned, as required by the act of Assembly, proposed to ask the witness : “whether the assignment of the account had or had not been made, because of its being barred by limitations; and for the purpose of making himself a witness to prove the rendition of the services charged therein; and the promise of the defendant’s intestate to pay the same.” The counsel for the plaintiff objected to this question being propounded to the witness, and the objection having been sustained by the court, the correctness of their opinion, in this respect, becomes also the subject of examination.
It is clear, that it was competent for the defendant, on the pleadings in the cause, to prove that the account in question had not been bona fide assigned, as required by the act of Assembly of 1829, ch. 51. The suit was brought in the name of the assignee, under the provisions of that statute, which enables the bona fide assignee of a chose in action, for the payment of money, to maintain an action in his own name. The objection, that the plaintiff was not a bona fide assignee of this account, and was not therefore embraced by the provisions of the act of Assembly, went directly to his right to recover, and was admissible upon the plea of non assumpsit. The assignment was necessarily exhibited by the plaintiff, as constituting his title to sue, and was liable to be attacked by his adversary, on the ground of the fraudulent character of the transaction.
It has, however, been contended by the counsel for the appellee, that the evidence proposed to be offered, was inadmissible, because the effect of it was to contradict, or explain the terms of the written assignment. And in support of the proposition, the cases of Bend against The Susquehanna Bridge Company, 6 H. & J., 128; Watkins vs. Stockett, 6 H. & J., 444; and Westly vs. Thomas, 6 H. & J., 24; have been referred to. Those cases recognise the familiar principle, that it is not in the power of a party, except on the ground of a fraud or mistake, to contradict by parol evidence the instrument which he has signed, or to interpolate into it, new terms and stipulations.
*220But a clear view of the object for which this testimony was offered, will show, that its admissibility was unaffected by the decisions to which we have been referred; and, that it is not obnoxious to any just exception. It was not proposed for the purpose of contradicting the assignment, or of ingrafting upon it any new or additional consideration. The defendant admitted that the assignment was purely voluntary, and that the proceeds of the account, when collected, were to be applied by the trustee, for the exclusive benefit of the cestui que trusts. The question propounded to the witness, was to discover the motive by which he was governed in making the transfer, and to prove that it was for the purpose of enabling the assignor to become a witness, and thus remove the bar raised by the statute of limitations. An assignment made under such circumstances, cannot be regarded as, bona fide, within the meaning of the act of Assembly. And when it is considered, that the testimony was offered, not by a party to the instrument, but by a stranger, and one who was injuriously affected by the assignment, and upon the ground that it was founded in fraud, we can perceive no reason for rejecting it.
The rule indeed, which has been relied on, as forbidding the introduction of parol evidence to contradict or vary the terms of the written assignment, has no application to this case. It is confined to the parties to the instrument, and their representatives, or those claiming under them; and does not extend to a third person, in the situation of the defendant. 1 Wheat. R., 314. 1 Greenl. Ev., 317.
It is true, as stated by the counsel for the appellee, that the court will not permit the assignor to defeat, or disparage, the title of his assignee, by acts or admissions, subsequent to the assignment. The assignee, even in cases where he is obliged to sue in the name of the assignor, is regarded as the real plaintiff. He is protected against “such acts and admissions of the assignor, as would operate in fraud of his rights.” Therefore, if the defendant should procure a release from the assignor, or obtain a sett-off against him, after notice of the assignment, or possess himself of any other defence, through his instrumentality, it would be inoperative; and the court *221would preclude the defendant from availing himself of such defence, “whether asserted in the form of a plea, or as evidence under the general issue.” Owings and Piet vs. Low, 5 G. & J., 145. Frear vs. Evertson, 2 J., 142. 5 Wheat., 277.
But this doctrine has no application to the question under consideration. The evidence was not offered to impeach the assignment, or to impair the rights of the assignee, by any thing that occurred subsequent to the transfer. It was proposed, as we have seen, to prove, that at the time the assignment was made, the assignor was influenced by considerations, which would invalidate the instrument itself, upon the true construction of the act of Assembly.
We are therefore of opinion, that the question proposed by the defendant was proper, and that the court erred in not permitting it to be propounded to the witness.
By the act of Assembly of 1829, ch. 51, to which we have already adverted, it is provided, “ that any assignee bona fide entitled to any judgment, bond, speciality, or other chose in action, for the payment of money, assigned in writing, may, by virtue of such assignment, maintain an action in his own name;” and the question presented for our consideration by the third exception, is, whether an open account of this description, is assignable, so as to authorise the assignee to sue in his own name, according to the true interpretation of that act?
It must be conceded, that an account for the rendition of medical services, and for the sale of medicine, is a chose in action for the payment of money; for, on proof that the services were rendered, and the medicine furnished, as charged, the law raises a promise to pay for them in money. As, therefore, an account of this kind is obviously within the words, it must be regarded as within the contemplation of the act, unless the legislature intended to discriminate between express and implied contracts. But no such distinction is to be found in the statute. The language is sufficiently comprehensive to embrace all choses in action, with the single qualification, that they must be for the payment of money; and the difference between an express and implied contract, is not in the cha*222racter of the undertaking, but only in the mode of proof. 2 Greenl. Ev. 78.
We think, therefore, that this account is embraced by the act of Assembly. Prior to that act, the assignee of a chose in action, unless it was negotiable by the mercantile law, was obliged to sue in the name of the assignor, or if he was dead, in that of his personal representative. To obviate this inconvenience, often injurious to the assignee, the act of Assembly was passed; and is to be liberally construed, as a remedial and beneficial statute.
The elementary writers upon the subjects of contracts, divide them into two classes: those, in which the parties stipulate to perform, or to omit to do, some act or duty, and those which are for the payment of money. The former class of contracts is clearly not within the provisions of this act of Assembly; for, though the law gives to the party a remedy in the form of damages for the injury he sustains by a violation of the contract, it is not a chose in action for the payment of money.
In the case of Gordon against Downey, 1 G. R., 41, the chose in action was a written agreement, by which the defendant stipulated for the payment of a rent, in money, to the lessor of the demised premises, and also to give to a third person mentioned in the instrument, a portion of the produce raised upon the land, and to furnish the means of removing it.
It is apparent, therefore, from an inspection of the agreement, that it was not a chose in action, purely for the payment of money, but contained other stipulations; and upon this ground, the court held that it was not such a chose in action as was contemplated by the act of Assembly. They say: — "It was not the intention of the legislature to confer on the assignee any such power, except in cases where the chose in action was purely for the payment of money; and where the only action which, from the nature and stipulations of the chose in action assigned, the assignor could have maintained, if no assignment had been made, was that for the payment of money due on the contract.” This is the character of the chose in action before us. It is evident, that the only action which the assignee could have maintained on this account, if no assignment had *223been made, was an action for the payment of money, due on the implied contract.
It follows from the views thus expressed, that we think, the court below committed no error by rejecting the defendant’s prayer, as presented in this exception. The plaintiff was entitled to maintain the action in his own name, by virtue of the assignment, and it was unnecessary either to aver in the declaration, or prove, a promise by the defendants to pay the account.
We think the court below decided correctly in overruling the motion made by the defendant to arrest the judgment. Tha,t it was not necessary for the plaintiff to aver in his declaration, that he was bona fide, entitled to the account, or that it was bona fi,de assigned, is determined in the case of The Bank of the United States vs. Lyles, 10 G. & J., 326. The objection would have been bad on demurrer.
We concur therefore with the county court, in the opinion expressed by them in the first and third exceptions, and in overruling the motion in arrest of judgment. But as we dissent from the opinion expressed by the court in the second exception, we shall reverse the judgment, with costs to the appellant, and order a procedendo.
JUDGMENT HE VERSED AND PROCEDENDO AWARDED.