Abstract
SUMMARY: Stable protoplasts may be released from Micrococcus lysodeikticus and Sarcina lutea by digestion of the cell-wall with lysozyme in sucrose or NaCl solutions having an osmotic pressure of some 25 atmospheres, but not in glycerol solutions of the same osmotic pressure. The stability of the protoplasts depends not only upon the depression of the water activity by the solute but upon an osmotic pressure exerted against the protoplast (plasma-) membrane. The permeability of the protoplast membrane to a number of solutes resembles that of the osmotic barrier of intact Staphylococcus aureus.