MacfarlanD: The report of the committee appointed to survey the instrumental aids to hearing, in Aids to Hearing. Washington, DC, American Federation of Organizations for the Hard of Hearing, 1927, p 39.
4.
MacfarlanD: The report of the committee appointed to survey the instrumental aids to hearing. Volta Rev29:592–629, 1927.
5.
HughsonWRegerS: Use of hearing aids. Trans Am Acad Ophthalmol Otolaryngol48:287–288, 1943–1944.