A detailed description of the structure of Amoeba of the proteus type. The author concludes that in one portion, the plasmagel, a typical Butschlian alveolar structure exists, and in another, the plasmasol, a typical emulsion, the one essentially solid, the other essentially liquid; but that this difference in structure cannot be very significant for during locomotion the one changes continuously into the other and vice versa. He further concludes that "water and proteins and oxygen and salts and all the other chemical compounds known to be associated with vital processes are quite as much alive as any other compounds, no matter how complex they may be"; that "the essence of being alive consists in organization rather than in specific substance"; and that "the essentials in the structure of protoplasm consist neither of solidity nor fluidity nor elasticity, but of a subdivision into innumerable compartments, each partially chemically isolated from the other and from the surrounding medium, a subdivision which may obtain in an emulsion or in a suspension, as well as in an alveolar system, or a structure consisting of discrete interlaced fibers with more fluid substance between them.".