ABSTRACT
IN the simplest single cell it is possible to observe a definite limit at which it is separable from its surroundings: as we have said, to the ordinary man it has an inside and an outside. The inside apparently is not all of the same kind or form, not, so to speak, like a bottle absolutely full of oil, or a cylinder absolutely full of oxygen at the same pressure everywhere: it is as though several kinds of material in several forms were present in the protoplasm of the inside of the cell. There is a nucleus (a centre of activity), sometimes a nucleolus (a smaller edition of the nucleus), some apparently rod-like structures, and some small ‘empty’ spaces (or vacuoles). One may justly regard all these component parts as coexisting for common advantage: they form a simple community.
