1. Barber, H. (1912). Practitioner, 89, 230.
2. Traitepratique d'Auscultation, 2e;Barber, H.,1938
3. Bean, W. B. (1937). Amer. Heart J., 14, 684.
4. Beck, C. S. (1935). J. Amer. med. Ass., 104, 109.
5. Acta medica et philosophica. Hafniensia IV. Obs;Borch, 0;XLVII,1676