Hasselbach, Wilhelm Emeritus Group Biophysics, Max Planck Institute for Medical Research, Max Planck Society;
http://www.sciencedirect.com/science/article/pii/S0079610764800067/pdf?md5=3cabf9e6699360efeeb0b1eaad98c9dd&pid=1-s2.0-S0079610764800067-main.pdf (Any fulltext)
https://doi.org/10.1016/S0079-6107(64)80006-7 (Any fulltext)
Hasselbach, W. (1964). Relaxing factor and the relaxation of muscle. Progress in Biophysics and Molecular Biology, 14, 167-222. doi:10.1016/S0079-6107(64)80006-7.