398 PROF. TH. W. ENGELMANN. 



The visible phenomena resulting from artificial stimulation 

 may vary to a very great extent. We must here consider especi- 

 allv whether the protoplasm was in movement at the time of 

 the excitation or not, and in the former case the kind and 

 energy of the movement ; further, whether the protoplasm was 

 excited at the same time all over and to the same extent, more 

 especially whether the stimulation was stronger at some spots 

 than at others ; further, whether it was free to move or was 

 shut in a firm cell-wall, &c. The following special obser- 

 vations give some idea of the manifold character of the phe- 

 nomena. 



Generally, the effect of artificial stimulation shows itself in 

 the directly excited portion of the protoplasm receding without 

 visible change of volume, drawing itself together so as to expose 

 the least possible external surface, and taking on a spherical 

 form, just like a stimulated muscle. The rapidity and power 

 with which it does this generally range within the same limits 

 which exist for the spontaneous movements of the same object. 



1. Electrical Stimuli. 



Electrical currents only cause a movement in protoplasm 

 when they flow directly through it, never from a distance 

 only.^ Moreover, it is especially sudden changes in the inten- 

 sity of a current which are followed by movements. The 

 change in the current, as in the case of muscles, is not nearly 

 so important as is the occurrence itself of the current, 

 but after the breaking of a constant current, responsive move- 

 ment takes place, as a rule, only in those cases where the 

 current, after attaining its full force, has continued to flow 

 for some time.^ 



This time may amount, as in the case of Amoeba, to more 

 than a second. KUhne^ observed in Actinosphaerium that 



* Becquerel (' Conipt. rend.,' 1837, ii, p. 786) found strong galvanic streams 

 (10 — 30 elements) quite' inactive when passed through a wire bound round 

 Chara, whatever the direction of the current. 



2 Th. W. Engelmann, " Beitrage zur allgem. Muskel und Nervenphysiolo- 

 gie," ' Arch. f. d. ges. Physiol.,' iii, pp. 311 and 312, 1870. 



' Kuhne, 'Unters. iiber das Protoplasma,' p. 59, et seq. 



