we may look upon the metabolic equilibrium as a special, although a very highly complicated, instance of chemical equilibrium, and we may explain the metabolic self-regulation following a dissimilative excitation of the same, by those principles on which the rebuilding of chemical equilibrium is founded. It is true that the special details of this process can be differentiated in only that degree in which it is possible to penetrate at all into the details of metabolism of the given cell form. In this, as is well known, the advance is extremely slow. The rebuilding process following decomposition of living substance in response to an excitating stimulus consists not merely in compensation for the decomposed atom groups but also in the removal of disintegration products. This removal can be accomplished, in so far as simple chemical substances such as carbon dioxide and water are concerned, by diffusion. Observations have shown that the semi-permeable protoplasm surface is pervious to water and carbon dioxide. The latter can, therefore, depending upon the amount of concentration, be eliminated from the living substance. Output of water likewise takes place in so far as the specific water content of the living substance is exceeded and which is osmotically regulated by its amount of salt content. When, finally, osmotic pressure within the living cell and in the surrounding medium is equal, the interchange of water ceases. All these processes are explained by diffusion. Self-regulation takes place in this regard simply by osmotic means. The conditions in respect to those decomposition products consisting in more complicated organic combinations, such as lactic acid, fatty acids and nitrogen derivatives of protein disintegration, are somewhat different in that the protoplasm surface possesses the property of hindering the passage of these substances into the medium. These are, as is well known, first transformed by secondary chemical processes into transfusable substances. In this transference the oxydative decomposition with the formation of simpler substances plays the most important rôle, so that the substances thereby formed, namely, carbon dioxide, water and ammonia, are osmotically eliminated as the result of the selective permeability of the surface of the protoplasm. In this way the living cell rids itself of the useless products of metabolism.