Colloids pass insensibly into crystalloids on the one hand and into coarse suspensions (water shaken up with fine mud, for instance) on the other. We may replace the concept of a colloid by those of “suspensoids” and “emulsoids.” A suspensoid is a liquid containing particles in a fine state of division--if the division is that into the separate molecules we have a solution, if into large aggregates of molecules we have a suspension. If the substance in the liquid is itself liquid, the whole is called an emulsoid. On the one hand this approaches to a mixture of oil in soap and water--an emulsion--and on the other hand to such a mixture as chloroform shaken up with water, when the drops of chloroform readily join together so that two layers of liquid (chloroform and water) form. What we see, then, in protoplasm is a viscid substance possessing a structure of some kind, and containing specialised protoplasmic bodies in its mass (nuclei, nucleoli, granules of various kinds, chlorophyll, and other plastids, etc.). It may contain or exhibit suspensoid or emulsoid parts or substances, or it may contain truly crystalloid solutions. These phases of its constituents are not fixed, but pass into each other during its activity. Nothing that we know about it justifies us in speaking about a “living chemical substance.” On analysis we find that it is a mixture of true chemical substances rather than a substance. It is no use saying that in order to analyse it we must kill it, for what we can observe in it without destroying its structure or activities indicates that it is chemically heterogeneous. This is not a textbook of general physiology, and the examples of physico-chemical reactions in the organism which we have selected have been quoted in order to show to what extent the chemical and physical methods applied by the physiologists have succeeded in resolving the activities of the organism. The question for our consideration is this: do these results of physico-chemical analysis fully describe organic functioning? Dogmatic mechanism says “yes” without equivocation. Now it is clear, from even the few typical examples that we have quoted, that physiological analysis shows, indeed, a resolution of the activities of the organism into chemical and physical reactions. How could it do otherwise? How could chemical and physical methods of investigation yield anything else than chemical and physical results? The fact that these methods _can_ be applied to the study of the organism with consistent results shows that their application is valid; that we are justified in seeing physico-chemical activities in life. But are these results _all_ that we have reason to expect?