THE CHARACTERISTICS OF STIMULI 59 



concisely : the effect of the stimulus never wholly disappears 

 unless the changes in the external vital conditions return to their 

 original state. 



But more, an effect of the stimulus cannot indeed take place 

 without a certain duration of stimulation, which is related in its 

 turn to the rapidity of reaction of particular living system. This 

 can be much more readily observed in more slowly reacting sub- 

 stances. Pick 1 first proved this fact on the muscle of the Ano- 

 donta. I have also been able to demonstrate the same fact in the 

 slowly reacting sea rhizopods 2 by the use of the constant current. 

 When Orbitolites is stimulated with a constant current lasting 

 approximately the tenth of a second, no response is seen in its 

 extended pseudopods, which are directed towards the poles. 

 The same is the case if the induction current is employed. Only 

 when the constant current of the uniform strength lasts 

 approximately .05 seconds, a barely perceptible response occurs, 

 manifested by the sudden stoppage of the centrifugal flowing of 

 granules in the anodic pseudopods, which, however, after the 

 lapse of one to three seconds continues again unaltered. Should 

 the duration of the constant current be still further prolonged, 

 typical symptoms of contraction are seen being manifested by a 

 heaping up of the protoplasm in the pseudopods in the form of 

 spindles and balls, whilst the protoplasm flows in a centripetal 

 direction towards the central cell body. (Figure 7.) 



Two effects can be realized by the alteration in the living 

 system as the result of prolonged stimulation. Either a new 

 state of equilibrium is established by the prolonged action, or 

 sooner or later death develops. In considering both results, how- 

 ever, we will ignore for the present the fact that every living 

 system in the absence of such prolonged stimulation is always in 

 a state of change, i.e., development. Only with this restriction 

 can an equilibrum of the living system be spoken of. 



1 A. Pick: "Beitrage zur vergleichenden Physiologic der irritablen Substanzen." 

 Braunschweig 1863. 



The same: "Untersuchungen iiber die electrische Nervenreizung." Braunschweig 

 1864. 



2 Max Verworn: "Untersuchungen iiber die polare Erregung der lebendigen Sub- 

 stanz," etc. Ill Pflugers Arch. Bd. 62, 1896. 



