The increase in volume under the influence of stimuli further shows the relation between the group of those solely catalytic effects of stimulation consisting in mere alterations of rapidity of the specific vital process, and that of the metamorphotic effects of stimulation, which manifest themselves in qualitative alterations of the vital process. Simple observation shows us that a qualitative change of individual constituent processes must necessarily result from the increase of volume of a cell, and that considering the close correlation of all the individual processes a profound alteration of the entire metabolism must be produced. I have already at another place[52], [53] treated these conditions more in detail and will, therefore, only briefly refer to them here. If we study the growth of a ball-shaped cell, we find that the surface then increases as a square, and the volume as the cube. It therefore follows that, by progressive volume increase, the conditions for the interchange of substance with the surrounding medium must become more and more unfavorable for those cell portions situated in the interior, whereas those at the exterior are at much greater advantage. This must lead to a constantly increasing difference of the rapidity of the metabolic processes between the peripheral and central portions. Accordingly, the intricate interworkings of the individual constituent processes, the rapidity of action of all which is intimately connected, are, therefore, followed by corresponding alterations in the entire metabolism. Sooner or later a stage is reached in which the individual constituent processes become so limited that certain metabolic products, which previously were broken down as soon as formed, can be no longer eliminated and remain in the cell acting as foreign bodies. In this way the relative quantity of the individual cell substances become more and more altered, and as the course of chemical processes occurs in accordance with the law of mass action, the whole metabolism is directed into another channel, so that finally new constituent processes take place, which were formerly not possible. These in their turn produce deep-seated alterations of the relations of the cell to its surrounding medium, etc. Hence this mere increase of volume of the cell in growth forms the source of an infinite mass of alterations in the activities of cell metabolism, which we briefly term its “_development_,” and which by constant progression, leads either to a process of cell division, and with this to a correction of existing disorder, or finally to irreparable disturbances ending in death. In this way an inseparable relation exists between increase of volume and the development of living substance. We have seen, however, that the catalytic reactions of stimulation, which at first only produce an alteration of rapidity of the individual constituent processes, if of prolonged duration