particles have a negative charge can be caused to coagulate (go into the gel stage) by one of two means: either by positively charged ions, or by the positive electrode of a battery. The coagulating effect of ions increases with their valency, and much more rapidly than the valency. The most valuable among Hardy's discoveries is the fact that in a solution of white of egg the colloidal particles can be rendered either positively or negatively electric by the addition of hydrogen or hydroxyl ions. When the neutral or isoelectric point is reached, the slightest change—one feels almost inclined to use the word 'stimulus'—is sufficient to transform the solution into a gel.
But long before the critical point of a colloidal solution is reached the variation in the charge of the colloidal particles alters their physical properties. An increase in their charge has the same effect as if the viscosity of the liquid were increased.
The bulk of our protoplasm consists of colloidal material, and the physical manifestations of life, such as muscular contractions and protoplasmic motions, and the innervations, are due to changes of the condition of these colloidal solutions. We now may be able to understand why the electrical current is the universal form of stimulation. The reason may be that the particles in colloidal solutions are electrically charged, and that every alteration of the charge of the particles will result in a process of innervation or a contraction or protoplasmic motion, etc. We likewise understand why the ions, on account of their electrical charges, are equally well capable of altering the physiological properties of the tissues, as the galvanic current.
But how can the ions cause toxic and antitoxic effects through their electrical charges? In my preliminary notice on these experiments which appeared in Pflüger's Archiv in November, 1901, I pointed out the possible relation of the electrical charges to the viscosity of the protoplasm. Phenomena of cell division are, as I believe with Bütschli and Quincke, phenomena of protoplasmic streaming. Such phenomena require, as Quincke has shown, a definite degree of viscosity. If the viscosity is too great, no protoplasmic motion is possible, and the same is true if the viscosity is too small. It may be possible that the toxic charges—presumably the negative one in the case of sodium salts—alter the viscosity of the protoplasm by either making it too liquid or too viscous, thus preventing the protoplasmic motions necessary for cell division or the muscular contraction. Small quantities of oppositely charged ions with a higher valency, which give off their charge sufficiently readily, will act as antitoxic substances.
2. The thermodynamical theory of life phenomena has utterly failed to show how the thermal energy produced through the splitting up and oxidation of foodstuffs can lead to muscular contraction. Engelmann's well-known attempt at an explanation is based on a physical impossi-
