Mistake as to a fact may operate to render the contract invalid.1

A mistake as to a matter of opinion does not avoid the contract.2 A release of damages for personal injuries which is executed under nell, a mutual mistake of the parties as to the length of time required for the injured person to recover from his injuries is valid.3 A mistake as to the existence of evidence is not a mistake of fact for which a contract may be treated as invalid.4 135 la. 555, 124 Am. St. Rep. 309, 113 N. W. 344 (fraud).

Maine. Neal v. Coburn, 92 Me. 139, 69 Am. St. Rep. 495, 42 Atl. 348 (fraud).

Michigan. Gawntlett v. Sea Ins. Co., 127 Mich. 504, 86 N. W. 1047.

Minnesota. Stong v. Lane, 66 Minn. 94, 68 N. W. 765 (said to be voidable).

Missouri. Nordyke, etc., Co. v. Keh-lor, 155 Mo. 643, 78 Am. St. Rep. 600, 56 S. W. 287.

New Hampshire. Russe) v. Clough, 71 N. H. 177, 93 Am. St. Rep. 507, 51 Atl. 632; Concord Coal Co. v. Ferrin, 71 N. H. 33, 93 Am. St. Rep. 496, 51 Atl. 283.

New York. Duncan v. N. Y. Mutual Ins. Co., 138 N. Y. 88, 20 L. R. A. 386, 33 N. E. 730.

North Carolina. Burton v. Rosemary Mfg. Co., 132 N. Car. 17, 43 S. E. 480.

Ohio. Hamet v. Letcher, 37 O. S. 356 (fraud).

Pennsylvania. Fink v. Smith, 170 Pa. St. 124, 50 Am. St. Rep. 750, 32 Atl. 566.

Wisconsin. Walker v. Ebert, 29 Wis. 194, 9 Am. Rep. 548.

For the effect, in general, of mistake, see Mistake in the Formation and Performance of a Contract, by Roland R. Foulke, 11 Columbia Law Review, 197,

299; Mistake of Fact as a Ground for Affirmative Equitable Relief, by Edwin H. Abbot, Jr., 23 Harvard Law Review, 608; Essential Error, by H. Burn Murdoch, 22 Juridical Review, 222; A Critical Analysis of the Law as to Mistake in its Effect upon Contracts, 38 American Law Review, 334. See also, The Effect of Mistake on Delivery of Chattels, by R. S. Wright and the Editor, 2 Law Quarterly Review, 313.

The general rule is subject to some qualification as to the effect of negligence. See Sec. 272.

2 "The difficulty in every case is to determine whether the mistake or misapprehension is as to the substance of the whole consideration, going, as it were to the root of the matter, or only to some point, even though a material point, an error as to which does not affect the substance of the whole consideration": Kennedy v. Mail Co., L. R. 2 Q. B. 580, 588 [quoted in Sherwood v. Walker, 66 Mich. 568, 577, 11 Am. St. Rep. 531, 33 N. W. 919].

1 See Sec. 251.

2 Seymour v. Chicago & N. W. Ry. Co., 181 la. 218, 164 N. W. 352; Nelson v. Chicago & N. W. R. Co., 111 Minn. 193, 20 Am. & Eng. Ann. Cas. 748, 126 N. W. 902.