delivered the opinion of this Court.

The exceptions brought up on this appeal are taken to the refusal of the Court below to permit the evidence offered by the appellant (the plaintiff below), and other evidence elicited by the appellee, on cross-examination of the appellant as a witness, to be considered by the jury.

. The first exception referring to the pleadings, it is proper to state them briefly.

The amended nar of the plaintiff contained three counts; the first, on a promissory note, described therein as joint and several, and dated the 31st of May, 1864, then over due, for four hundred and twenty dollars, payable to the plaintiff ninety days after date.

The second, for money payable by the defendants to the *47plaintiff, for goods bargained and sold; the third, for money found to be due from the defendants to the plaintiff on an account stated between them. The defendants, as to the first, second and third counts, pleaded “ they were never indebted as alleged and for a second plea to the first count, the defendants say, “ they never promised as alleged on which several pleas issues were joined.

The appellant, to maintain the issues on his part, having first proved its execution, offered the following paper:

“ $420.00. Frederick County, May 31st, 1864.

■ “Ninety days after date, we, or either of us, promise to pay to Charles E. Myers, four hundred and twenty dollars, being the balance due on the crop of wheat purchased by us from said Myers, with this express understanding and agreement, that should loss or difficulties occur from any cause whatever, by any person or persons claiming an interest or portion of the share of said Myer’s interest in the wheat crop aforesaid, on the farm of Col. Jacob M. Kunkel, on which Myers lately resided, then and in that event, such loss or deduction to be taken from the amount to be paid by this note.

“John Smith, of M.

“John W. B amuck.”

To which the appellees objected as inadmissible under the pleadings in the cause, which objection the Court sustained and the appellant excepted, which constitutes the ground of the first exception.

If this instrument had been offered by the appellant to maintain the issue joined on the first count in the nar only, which declares on a promissory note, the objection to its admissibility would have been well taken, for the paper does not amount to a valid promissory note, not being a promise for a fixed and certain amount, but for an amount subject to vary upon certain contingencies. *48Vide Story on Promissory Notes, sec. 20 ; Bayley on Bills, ch. 1, sec. 4, p. 11 (5th Edition). Story on Bills, sec. 42. 20 Pick. Rep., 132.

But the paper was offered, to support the issues generally, and if admissible upon either of the issues, it was error to reject it entirely.

Being a promise to pay a liquidated sum, after a period then passed, as a balance due for goods sold and delivered, it was prima fapie evidence under the second count, subject to the deducting referred to therein, upon proof of the happening of the loss or difficulties if any.

It was"incumbent on the defendants to show what loss had occurred, to entitle them to the deductions stipulated in the agreement. It did not appear when the paper was offered that any such had occurred. If such losses had appeared, it was no ground for rejecting the evidence, but entitled the defendants to an abatement pro tanto. We think the Court below erred in excluding the paper under these circumstances.

The second exception arises as follows :

The former testimony having been offered and rejected, the plaintiff was offered as a witness, and detailed all the particulars of a verbal contract entered into between himself and John Smith, of M., about one week prior to the 31st of May, 1864, in which it was agreed that Smith would buy the plaintiff’s interest in a crop growing on a farm of Jacob M. Kunkel, sown in the autumn of 1863, and to be cut during the harvest of 1864 ; that Smith was to discharge the duties of the plaintiff to his landlord, by cutting and securing one half for the benefit of Kunkel, and to have for himself the other half, for which he agreed to pay $840. In a day or two afterwards, Smith told the plaintiff that the defendant, Barrick, was partner with him in the purchase of the crop. On the morning of the 31st of May, 1864, the plaintiff met the defendants, Smith and Barrick, and it was agreed amongst all the *49parties that Smith and Barrick purchased plaintiff’s interest in said wheat for the sum of $840; on the same day the defendants paid plaintiff $420, in part of said purchase money ; the defendants did, during the harvest of 1864, cut and secure said wheat crop and take to themselves one half thereof.

The defendant, then, ora cross-examination of said witness, proved by him that on the 31st of May, 1864, the balance of the said sum of $840, after payment of said sum of $420, was secured by a written paper, and that the terms of payment Avere expressed in said paper ; that said terms expressed in said paper, had not been mentioned by any of the parties Avhen the contract for sale of said interest in said Avheat crop was made, and not until after the said $420 had been paid, but were mentioned afterwards and agreed to by plaintiff. That no other contract than that Avhieh Avas reduced to writing as aforesaid, was entered into by said parties on that day, relative to the unpaid purchase money for said Avheat, which is sought to be recovered in this action. Whereupon the defendants moved the Court to Avithdraw from the consideration of the jury all that portion of the testimony of the plaintiff relating to the unpaid purchase money for said wheat, because it appears from the testimony of the said witness that the contract for the payment thereof, and the terms on which it was to be paid, Avere reduced to writing and signed by the defendants, and it is not competent for the plaintiff to give parol proof thereof, Avithout producing the Avritten contract, Avhieh motion the Court granted, and the plaintiffs excepted. This ruling of the Court beloAV is excepted to in the appellant’s brief, on the ground that it Avas too late to object to the testimony of the plaintiff,under the circumstances of his examination in this case; to which the appellees reply, that the objection Avas raised as soon as it Avas made to appear that the facts, of which parol testimony had been given, Avere reduced to writing.

*50To our apprehension, as the facts áre presented by the record, the testimony of the plaintiff, relating to the terms of the agreement by which the unpaid purchase money was secured to be paid, being brought out by the defendants on cross-examination, it was not competent for them to object to it under the circumstances of this case. The paper, the non-production of which was the alleged ground of excluding the parol evidence of its contents, had been presented and proved by the plaintiff, and was excepted to and excluded at the instance of the defendants. There was no pretext of want of information of the existence, or of the contents of the paper, or of the identity of the agreement. These were apparent upon the face of the paper. The defendants drew out the facts with full knowledge that they had been reduced to writing.

The paper was not such an instrument as merged the antecedent parol contract. It was but a security for the payment of the balance o-f the purchase money, on a credit, which having expired, it was competent for the plaintiffs to sue on the original contract, notwithstanding the writing. It did not necessarily exclude other evidence.

“ The general rule is, that the acceptance of a security or undertaking of equal degree is, of itself, no extinguishment of the former debt. Thus the acceptance by a creditor from his debtor of his promissory note, for an antecedent simple contract debt, does not extinguish the original debt, (both being of equal degree in the eye of the law,) if it remain in the hands of the creditor unpaid and he can produce it to be cancelled or show it to be lost. But he will not be suffered to recover on the original cause of action, unless he can show the note to have been •lost, or produces it at the trial to be cancelled.” Glenn vs. Smith, 2 G. & J., 508 ; Wyman vs. Roe, 11 G. & J., 425. In the present case, as we have seen, the security was in Court, ready to be impounded. There being error *51in the rulings of the Court below, on both the first and second exceptions, the judgment must he reversed and procedendo awarded.

Judgment reversed and procedendo aioarded.