78 IRRITABILITY 



of the living substance. Sufficient importance has not as yet been 

 attached to this knowledge. This fact not only has a particular 

 interest for the much-discussed question of the source of muscle 

 energy, but also affords a deeper insight into the metabolic activity 

 of the living substance. It shows us that we must not imagine 

 a purely linear linking of the individual constituent metabolic 

 processes, but rather, at least at certain points, a branching forma- 

 tion, the individual members spreading in various directions. An 

 alteration in an individual member can occur without an imme- 

 diate change in the other branches. This would not be the case 

 if there were only a linear connection of the constituent processes, 

 for the breaking of a single member of the chain would be 

 followed by a change in all the following members. 



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 pro- 

 ducing 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,^ in another field involving other condi- 

 tions 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.' 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 



1 Ehrlich: "Das SauerstoflFbedurfniss des Organismus. Eine farbenanalytische 

 Studie." Berlin 1885. Compare further: L. Aschoff: "Ehrlich's Seitenkettentheorie 

 und ihre Anwendung auf die kiinstliche Immunisirungsprocesse. Zusammenfassende 

 Darstellung." Zeitschr. f. allgemeine Physiologic, Bd. I, 1902. 



2 Max Verworn : "Die Biogenhypothese. Eine kritisch-experimentelle Studie uber 

 die Vorgange in der lebendigen Substanz." Jena 1905. 



