The Farm Credit Banks and the capital, reserves, and surplus thereof, and the income derived therefrom, shall be exempt from Federal, State, municipal, and local taxation, except taxes on real estate held by a Farm Credit Bank to the same extent, according to its value, as other similar property held by other persons is taxed. The mortgages held by the Farm Credit Banks and the notes, bonds, debentures, and other obligations issued by the banks shall be considered and held to be instrumentalities of the United States and, as such, they and the income therefrom shall be exempt from all Federal, State, municipal, and local taxation, other than Federal income tax liability of the holder thereof under the Public Debt Act of 1941 (31 U.S.C. 3124).