"SECTION 43. General Rule. - The taxable income shall be computed upon the basis of the taxpayer's annual accounting period (fiscal year or calendar year, as the case may be) in accordance with the method of accounting regularly employed in keeping the books of such taxpayer; but if no such method of accounting has been so employed, or if the method employed does not clearly reflect the income, the computation shall be made in accordance with such method as in the opinion of the Commissioner clearly reflects the income. If the taxpayer's annual accounting period is other than a fiscal year, as defined in Section 22(Q), or if the taxpayer has no annual accounting period, or does not keep books, or if the taxpayer is an individual, the taxable income shall be computed on the basis of the calendar year.

"SECTION 44. Period in which Items of Gross Income Included. - The amount of all items of gross income shall be included in the gross income for the taxable year in which received by the taxpayer, unless, under methods of accounting permitted under Section 43, any such amounts are to be properly accounted for as of a different period. In the case of the death of a taxpayer, there shall be included in computing taxable income for the taxable period in which falls the date of his death, amounts accrued up to the date of his death if not otherwise properly includible in respect of such period or a prior period.

"SECTION 45. Period for which Deductions and Credits Taken. - The deductions provided for in this Title shall be taken for the taxable year in which 'paid or accrued' or 'paid or incurred', dependent upon the method of accounting upon the basis of which the net income is computed, unless in order to clearly reflect the income, the deductions should be taken as of a different period. In the case of the death of a taxpayer, there shall be allowed as deductions for the taxable period in which falls the date of his death, amounts accrued up to the date of his death if not otherwise properly allowable in respect of such period or a prior period.