delivered the opinion of the Court.
The defendant having received the Houdlette note, in the course of his business, as the factor and agent of the plaintiff, and holding it afterwards in the same capacity, was bound to use due diligence in its collection. Fidelity in his trust, is imposed by the relation in which he stood. In all transactions of trade and commerce, the law requires promptness and vigilance oft the part of agents, and of all persons, who happen to be entrusted with the business of others. This is a principle too well settled, to require the citation of authorities for its support.. And if they were necessary, those cited by *403the counsel for the plaintiff, ara full to this effect. If from the want of diligence, by the factor, a loss arises to the principal, the factor is bound to make it good. If the jury were satisfied, that the Houdlette note was lost by a want of diligence on the part of the defendant, they were instructed that the defendant had no claim to he allowed the amount of that note against the plaintiff.
It was not incumbent on the plaintiff to give special directions, as to the course to be pursued by the defendant. That would depend upon what the exigency of the case required ; which the defendant, residing more in the neighborhood of Houdlette than the plaintiff, had the best means of knowing. But if that had not been the case, the business was deputed to him, and the plaintiff had a right to expect, that it would be faithfully performed. The plaintiff was under no obligation to pledge himself expressly, to reimburse any expense, the defendant might necessarily incur in bis business. This obligation the law imposed upon him, without a direct promise. We are therefore satisfied, that the instructions requested were properly withheld, and that those given to the jury, were warranted by law.
These are the only points reserved by the report; but as there is to bo a new trial, on account of newly discovered evidence, we have looked into the question, raised at the former trial, and insisted upon in argument by the counsel for the plaintiff, as to the admissibility of the evidence, upon which the defence turned.
It is an undoubted rule of the common law, that parol testimony shall not be received, to vary or contradict a written contract. In support of this principle, many cases have been cited. That the defendant did make the contract, declared on, is not to be controverted. It is a note of band, which like a specialty imports a consideration j and indeed acknowledges one. Shall this written acknowledgment Ise contradicted by parol evidence? The rule upon which the defendant relies, strictly understood, would exclude it. And yet that such evidence is admissible for this purpose, is as well settled as the rule. Between the decisions, which illustrate and enforce the rule, and those which recognize the exception, there *404may be an apparent discrepancy. But that will generally be found to arise, from the different aspects, in which they have been viewed.
The case of Barker v. Prentiss, 6 Mass. 430, and the opinion of Chief Justice Parsons there given, has maintained its ground in practice $ although the language used in subsequent opinions, cited for the plaintiff, appear sometimes to lose sight of the distinctions there made. The position laid down in that case is, that in all written simple contracts, evidence of the consideration may be received, between the original parties. And this is the uniform practice of our courts. If upon this inquiry it results, that there was no consideration $ or that it has failed totally or partially ; or that the contract was signed under mistake or misapprehension, the rights of the parlies are determined, as the justice of the case requires, upon a view of all the facts. The plaintiff fails to recover j or he recovers a part only, of what the note or other contract expresses ; according to equity and good conscience. Of this character was the evidence received, in the case before us. It went to the consideration. The lumber which formed part of the consideration of the note, was assumed to be worth a certain sum ; 'but its final value was to depend on the sales. If overvalued, there would be a failure of consideration, by the amount of the excess. If undervalued, the defendant was to pay the difference. As the estimate fell short of the value as ascertained, this part of the evidence operated in favor of the plaintiff.
- With regard to that part of the note in suit, which arose from the Houdlette debt, if that was not at the defendant’s risk, if lost without negligence imputable to him, there would be a failure of'consideration to that amount. Now the evidence proves that the defendant did not become the guarantor of the Houdlette note, and that it was not taken at his risk. It has been lost. That loss must fall upon the plaintiff; unless negligence in relation to it, is chargable upon the defendant.