Considering the close correlation of the individual part processes it would appear very strange, however, if a single one of these could undergo an alteration of its rapidity without the course of the rest of the processes being in the least influenced. One cannot comprehend such _absolute_ independence of a process brought about by functional stimulation from all the other constituent processes, particularly when this is of prolonged duration and involves to a considerable extent the alterations in rapidity, for the individual constituent processes are dependent in a high degree upon the quantity of the particular chemical substances of which the living system is composed. The cycle of the individual constituent processes of this system is determined in the most delicate manner in its rapidity and extent, by the relative quantities of the individual substances. Associated with an alteration in the rapidity of an individual constituent process, there would also be a relative alteration quantitatively of the substances. And with the increase in the _quantity_ of the disintegration products, and also the increase of the substances for their replacement, there would result, during this time, an alteration in the amount of interaction of the molecules of the other constituent processes, so that these processes secondarily suffer an alteration in rapidity which is perceptible after long continued involvement of the functional part of metabolism. In fact, in the previously mentioned case of the functional stimulation of the muscle, the proof has been furnished that a long-continued increase of the functional metabolism is followed, although to a less extent, by an increase in the entire cytoplastic metabolism. _Argutinski_ showed this on himself in 1890 in _Pflüger’s_ laboratory. He found, namely, that after the exertion of a long walk in a hilly district, a considerable increase of nitrogen excretion in the urine took place, which extended over the succeeding two or three days. This increase of the nitrogen metabolism in its totality is not nearly as great as that of the breaking down of nitrogen-free substances, but it is, nevertheless, present and shows us that functional metabolism cannot experience a lasting excitation without being followed by secondary results in the entire cytoplastic metabolism. This fact is even more strikingly illustrated in the alteration of the entire volume of a living organism as produced by the lengthened duration of functional stimulation. It has been long known, that the muscle as the result of frequent functional excitation by means of adequate nerve impulses, that is, prolonged activity, is considerably increased in size, whereas in the absence of such it loses more and more in volume. A hypertrophy of activity, produced by functional stimuli, and the atrophy of inactivity, the result of the discontinuance of the functional excitation, is universal and can be observed in the various tissues of our body.