1. Einthoven, W., Fahr., G., and de Waart, A. (1913). Pflulger's Arch. Physiol., 150, 275.
2. Lyle, A. M. (1944). Amer. Heart J., 28, 199.
3. Myers, G. B., and Oren, B. G. (1945). Amer. Heart J., 29, 708.
4. Norris, G. L., and Massie, E. (1947). Proc. Central Soc. Clin. Research, 20, 57.
5. Personal communication;Shillingford, J.; Leatham, A.,1950