It shows us, further, that certain branches are more labile than others. In the case referred to here, the branches of this system, which bring about the nitrogen metabolism, are relatively _firm_ and _stable_, the branches, which are disturbed by the stimulus producing functional activity of the muscle, are particularly _labile_. I should like in passing to call here your attention to the fact that as is well known, _Ehrlich_,[49] in another field involving other conditions and other experiences and considerations, has arrived in analogous manner at his “side chain theory.” In order to have an expression for those stimuli which involve rapid alteration of the labile constituent processes and which are connected with the specific action of the particular organism, I have called them “_functional stimuli_,” and contrasted with them the “_cytoplastic stimuli_.” In the latter the alterations produced include all the constituent processes extending even to the stable processes of nitrogen changes, and sometimes extend to complete disintegration and rebuilding of living substance.[50] To the first group belong all adequate stimuli within certain limits of duration and intensity, and the greater part of inadequate stimuli of brief duration so long as they do not exceed a certain intensity. To the latter group belong in general all the stronger adequate and inadequate stimuli of prolonged duration; such as extreme temperature, the stronger electric currents, constant alteration in the supply of food, water, oxygen, the prolonged or stronger influence of extraneous chemical matter, etc. [49] _Ehrlich_: “Das Sauerstoffbedürfniss des Organismus. Eine farbenanalytische Studie.” Berlin 1885. Compare further: _L. Aschoff_: “Ehrlich’s Seitenkettentheorie und ihre Anwendung auf die künstlichen Immunisierungsprozesse. Zusammenfassende Darstellung.” Zeitschr. f. allgemeine Physiologie, Bd. I, 1902. [50] _Max Verworn_: “Die Biogenhypothese. Eine kritisch-experimentelle Studie über die Vorgänge in der lebendigen Substanz.” Jena 1905.