The life of a cell is intimately associated with its salt environment, whether this is the sea, the soil water, or the body fluids. The classical experiments of Ringer on the biological effects of salts initiated the extensive research which has been done on the relationship between cells and their electrolytic environment. Our excuse for adding to the voluminous literature on this subject is that we have chosen an as yet little studied property of protoplasm, namely, extensibility, as the criterion by which to judge the effects of the salts.