(after stating the facts as above). Although the book account which was attached to and made a part of the complaint ostensibly begins on March the 5th, 1909, such account, in fact, was of earlier origin, and plaintiff, in order to make out its case and in order to avoid a payment which was made on May 29, 1909, disregarded its pleadings, and proved such account from its inception on the 11th day of August, 1908. In this new account was an item of some $182.82,, which was alleged to have been sold to the defendants on the 29th day of January, 1909, and to the payment of which plaintiff sought to apply the payment of May 29, 1909. The whole controversy, therefore, arises, over the question of whether on the 29th day of January, 1909, and prior to the said March 5, 1909, the plaintiff sold to the defendants a certain bill of goods, or whether such goods were, in fact, sold to a third party (Harrison), the defendants only agreeing to act as collecting; agents.
The principal assignment of error is that the court erred in instructing the jury that “in a civil action, before the plaintiff can recover, he must prove by a fair preponderance of the evidence the allegations of *287the complaint. That is, it places upon the plaintiff the burden of showing that he sold and delivered the goods to the defendants and defendants still owe him.” The plaintiff maintains that “the jury should have-been instructed that the defendants had pleaded payment, and that therefore the burden of proof was upon them to show by a fair preponderance of the evidence the facts upon which they relied as constituting such payment.”
Whether this would have been the fact or not under the case as originally presented by the pleadings, it is not necessary for us to determine. Nor is it necessary for us to criticize the somewhat informal answer which was filed in this case, and to say whether it contains both a general denial and a plea of payment or a plea of payment merely. All that it is necessary for us to say is that, in presenting its case, the plaintiff departed from its pleadings and introduced an entirely different account, and that, as no amendment to the pleadings was asked and no request made that the defendant should answer the new account which was sued upon, it must be presumed that the same was generally denied, and that, such being the case, the burden of proof to prove its-account was upon the plaintiff.
Attached to the original complaint and made a part of it was an account which began on the 5th day of March, 1909. Plaintiff, however, when it presented its case and in order to avoid a payment which it knew had been made on May the 29th, 1909, but for which it had given no credit in its account as originally filed, proved as a part of its own case the entire account from its inception on the 14th day of August, 1908, so as to be able to include therein the alleged sale on January 29, 1909, in the payment of which it sought to apply and to extinguish the remittance made on the 29th day of May, 1909, and thus leave to itself a balance of some $1'75./T2 due on the account from the 5th day of March, 1909.
In doing this, plaintiff practically interposed a new account and a new complaint. The issues were defined by the evidence. A denial would be presumed by the law, and under these issues the burden of proof was upon the plaintiff. Mott v. Baxter, 29 Colo. 418, 68 Pac. *288220; Pom. Code Rem. 3d ed. §§ 629, 700; Quinn v. Lloyd, 41 N. Y. 349; Brown v. Forbes, 6 Dak. 273, 43 N. W. 93; Powers v. Russell, 13 Pick. 69; Chicago, C. & L. R. Co. v. West, 37 Ind. 211; Fish & H. Co. v. New England Homestake Co. 27 S. D. 221, 130 N. W. 841; Hudson v. Hudson, 119 Ga. 637, 46 S. E. 874; 31 Cyc. 460."
“In an action on an account plaintiff’s account is not in its nature ■self-proving. . . . While as a general rule the burden of proving a negative averment is not upon plaintiff, yet . . . in an action on an open account for services plaintiff does not make [out] a case merely by showing . . . [the delivery of the goods and the value thereof]. Where the action is for the recovery of a general balance .' . . [upon a book account] upon which a payment is admitted, the full balance cannot be recovered without proof of all the items of debt, because there is no authority in such a case t'o apply the payments to any particular items of the account.” 1 C. J. 661, 662; Huffstater v. Hayes, 64 Barb. 573; Allen v. Brown, 11 Tex. 520.
Here the complaint was for a balance due on a book account, and ■contained negative averments of nonpayment which a denial, general ■or specific, would have put in issue. See Brown v. Forbes, 6 Dak. 273, 43 N. W. 93; Quinn v. Lloyd, 41 N. Y. 349; Mott v. Baxter, 29 Colo. 418, 68 Pac. 220; Pom. Code Rem. 3d ed. § 700; Knapp v. Roche, 94 N. Y. 329. The plaintiff proved as a part of its case, and sought to recover upon an account, the date of origin of which was prior to the .account sued upon. It asked for no new pleadings and went to trial ■on the new issue presented by it. A denial must be presumed, and the burden of proof was upon the plaintiff. This is not a case where a plea of payment was necessary and in which the burden of proof was therefore cast upon the defendant to sustain it. A plea of payment is only necessary where it interposes new matter. Brown v. Forbes, 6 Dak. 273, 43 N. W. 93; Sylvis v. Sylvis, 11 Colo. 319, 17 Pac. 912; Mott v. Baxter, 29 Colo. 418, 68 Pac. 220. In the case at bar, indeed, the new matter was sought to be interposed by the plaintiff, and not by the defendant.
Nor is there any merit in plaintiff’s objection to the question, “Now *289In the deposition taken here yon find a statement that on January 22, 1909, the Tolerton & Warfield Company sold you merchandise consisting of a thirty-day bill of goods, $71.65, and a sixty-day bill of .goods amounting to $6.39, and a sixty-day bill of goods amounting to $104.88 ?” This question was asked one of the defendants, and was ■objected to on the ground that it related to a transaction between the parties prior to the time mentioned in the complaint. Plaintiff’s agent, however, had not only testified to the transaction on his examination in chief, but had introduced in evidence in such examination the entire account between the parties, and which began, not on March 5, 1909, but on August 14, 1908. It was for the purpose of paying itself for this alleged account that the plaintiff had admittedly applied the payment of $182.82 which was made on May 29, 1909. We think there ■can be no question that when one sues upon a book account and alleges that it begins upon a certain date, or that the payments thereon began ■upon a certain date, and has excluded from such account a payment made after that date, and seeks to apply it upon a subsequent transaction, proof of the entire account can be introduced and all of the payments and credits therein during its whole existence. Lamb v. Hanneman, 40 Iowa, 41. And so, too, it is also to be noticed that the plaintiffs in their own deposition introduced evidence of this trans.action; and though we held in the case of Mulroy v. Jacobson, 24 N. D. 354, 139 N. W. 697, that the introduction by the defendant, without objection of letters, did not warrant the court in receiving in evidence letters or other evidence by the defendant which were objected to, we have nowhere held that a party may open the door himself and then object to evidence on the identical transaction to which he has testified, and especially when such transaction is necessarily included in his •cause of action.
Nor do we think the court erred in allowing the defendants to explain their letter of May the 29th, 1909, with which the payment of $182.82 was transmitted, and to say whether they intended the remittance to ■cover the Harrison bill, or merely to apply on the general account. This letter was as follows:
*290Tolerton Warfield Co., Sioux Oty, la. Marmarth, May 29, ’09. Checked June 1, 1909 Bookkeeper.
Gents: — ■
We send you ck in payt bills as follows:
$104.88
6.29
71.65
10.65
3.25
$196.72
We have not red a cent from the Harrison bills & as that bill was by your request you surely • will be willing to allow us a little time to collect it. Your man took the acct & we objected to it & he said you would send us a cr memo for 13%.
We are truly,
Marmarth Merc. Co.
The letter, at the most, was an admission against interest. The plaintiff sought to prove by it that the defendants had, in fact, bought the Harrison bill of goods, because the items of $104.88, $6.29, and $71.65 correspond with that bill. The defendants, on the other hand, contended that they merely intended to remit on the general account; that these amounts were taken from the files, and not from their books, and that when remitting it was not noticed that they related to the Harrison bills, which the defendants contended they had merely agreed to collect as agents, and not to guarantee or to assume. The rule that mistake must be specially pleaded does not apply where a person merely seeks to explain an apparent admission and to show his intention in making a payment. Nor are the defendants herein seeking to recover back money which was paid by mistake. They are merely seeking to have it properly applied.
From a perusal of the record we are not prepared to say that there *291is not sufficient evidence to support tbe verdict, and we axe satisfied tbat tbe matter was one for tbe jury, and not for tbe court, to pass upon.
Tbe judgment of tbe District Court is affirmed.