As used in this chapter, the term “unallocated interest fund” means the sum of (1) the earnings and profits accumulated prior to March 4, 1923, and attributable to investments and reinvestments under section 4312 of this title by the Secretary of the Treasury, plus (2) the earnings and profits accumulated on or after March 4, 1923, in respect of the earnings and profits referred to in clause (1) of this section.