1. Block, W. J., Crumpacker, E. L., Dry, T. J., and R. P. Gage, J. Amer. Med. Ass. 150, 259 (1952).
2. Cleempoel, H. et J. Enderle, Acta card. (Brux.) 11, 260 (1956).
3. Cole, D. R., Singian, E. B., and L. W. Katz, Circulation 9, 321 (1954).
4. Dietlen, H., Dtsch. Arch. klin. Med. 88, 55 (1907).
5. Döring, H. und R. Loddenkemper, Z. Kreislaufforschg. 51, 401 (1962).