The Secretary may, in accordance with section 238 of this title, accept conditional gifts for the National Institutes of Health or a national research institute or for the acquisition of grounds or for the erection, equipment, or maintenance of facilities for the National Institutes of Health or a national research institute. Donations of $50,000 or over for the National Institutes of Health or a national research institute for carrying out the purposes of this subchapter may be acknowledged by the establishment within the National Institutes of Health or a national research institute of suitable memorials to the donors.