1. Engström, A., and Lindström, B., Nature, 163, 563 (1949); Biochim. et Biophys. Acta, 4, 351 (1950).
2. Davies, H. G., and Wilkins, M. H. F., Cytochemistry Commission of the Society for Cell Biol. “Physical Aspects of Cytochemical Methods” (Stockholm, 1951); Nature, 169, 541 (1952).
3. Barer, R., Nature, 169, 366 (1952).
4. Dyson, J., Proc. Roy. Soc., A, 204, 170 (1950).
5. Davies, H. G., Wilkins, M. H. F., Chayen, J., and La Cour, L. F. (in the press).