In Wheeler W. Mfg. Co. v. Howard (C. C.), 28 Fed.R. 741, Mr. Justice BREWER said: "Where a mortgage provides that upon default in the payment of either of the notes secured thereby, all shall become 'immediately' due at the option of the holder, 'immediately due' means 'immediately upon or after the holder's election and he is not bound to elect immediately after default'." See also Damet v. Aetna Life Ins. Co. (Okla.), 5 A. L. R. 434, 179 Pac. R. 760. Waiver does not arise from forbearance for a reasonable time, but may be inferred from the mortgagee's passive acquiescence, from his knowledge of the sale of the property in violation of a condition, without making objection, from acts putting the debtor off his guard and leading him to believe that the right has been waived, or from his neglect to perform conditions binding on him, and on which his right to take advantage of the default is predicated; but not generally from loose declarations which he is under no obligations to make and on which no person relies to his prejudice.

In Luke v. Patterson, 192 Okla. 631, 139 P.2d 175, 148 A.L.R. 679, this court held that an acceleration clause authorizing the mortgagee to declare the entire indebtedness due, without notice, on failure of the mortgagors to pay an installment or taxes when due was legal and valid and may be relied on. Therein we also stated that such clauses were not objectionable as being in the nature of a penalty or forfeiture. See also Wheeler v. American Inv. Co., 167 Okla. 558, 31 P.2d 117; Damet v. Aetna Life Ins. Co., 72 Okla. 122, 179 P. 760, 5 A.L.R. 434, and 36 Am.Jur. Mortgages, Sec. 385. From our examination of the record we are of the opinion that the indulgence previously extended by plaintiff to defendants did not affect the right of plaintiff to enforce the acceleration clauses in the note and mortgage.

The mortgagee's right to exercise the option to treat the entire obligation due exists as long as the default continues. Damet v. Aetna Life Ins. Co., 72 Okla. 122, 179 P. 760. Ordinarily, the payment of delinquent taxes by the mortgagor will bar the mortgagee's right to exercise his option for acceleration (36 Am. Jur. 889 § 403; Fleming v. Franing, 22 Okla. 644, 98 P. 961); and the payment of past-due interest or installments will usually bar such right with respect to those particular delinquencies. 36 Am. Jur. 888, § 402.

"The authorities seem to hold that where, as in the case at bar, the creditor elects to enforce the accelerating clause and action is commenced upon the note and for the foreclosure of the mortgage, for default in the payment of interest, the note and mortgage constitute a single contract, which must be so construed as to give effect to all its parts, and when the mortgage provides that the note shall become due upon default in the payment of any installment of interest, such default renders the note due immediately, and entitles the holder to maintain an action at once for the entire debt. * * *" See, also, F. B. Collins Inv. Co. v. Sanner, 42 Okla. 634, 142 P. 318; Oklahoma City Dev. Co. v. Pickard, 44 Okla. 674, 146 P. 31; Phillips v. Williams, 33 Okla. 766, 127 P. 1072: Flesher v. Hubbard, 37 Okla. 578, 132 P. 1080; Damet v. Aetna Life Ins. Co., 72 Okla. 122, 179 P. 760. Defendant next contends that his verified general denial put in issue all the material facts alleged in the petition.

Such a provision for acceleration is permissive only and not self-executing; it makes the whole debt due and collectible only in case the mortgagee elects to exercise the option. 41 C. J. 413-414, 850; 19 R. C. L. 493-494, 496-497; Bollenbach v. Ludlum, 84 Okla. 14, 201 P. 982; Damet et al. v. Aetna Life Insurance Co., 72 Okla. 122, 179 P. 760; Moorehead v. Hungerford (Neb.) 193 N.W. 706.

Such language as is used in the note and mortgage means that the principal becomes due immediately upon exercise of the option. ( Tourny v. Bryan, 66 Cal.App. 426, 226 P. 21; Cook v. Strelau, 127 Wn. 128, 219 Pac. 846; Jump v. Barr, 46 Cal.App. 338, 189 P. 334; Damet v. Aetna Life Ins. Co., 72 Okl. 122, 5 A.L.R. 434, 179 Pac. 760; Hewitt v. Dean, 91 Cal. 5, 27 P. 423.) No waiver of the right of acceleration was pleaded in appellant's answer, and therefore such defense may not be set up. ( Washburn v. Williams, 10 Colo. App. 153, 50 P. 223.