Wis. Stat. § 25.70

There is established a separate nonlapsible trust fund designated as the historical society trust fund, consisting of all endowment principal and income and all cash balances of the historical society. Unless the board of curators of the historical society determines otherwise in each case, only the income from the assets in the historical society trust fund is available for expenditure. In this section, unless otherwise provided in the gift, grant, or bequest, principal and income are determined as provided under subch. XI of ch. 701.