STIMULI AND THEIR ACTIONS 



423 



Expansion -effects of galvanic stimulation are mostly incon- 

 spicuous externally, and it has already been seen that only in 

 certain cases is it possible to observe them at all. But contraction- 

 effects are everywhere noticeable. Typical phenomena of contrac- 

 tion have already been seen in Actinosphcerium and Amphistegina in 

 the formation of globules and spindles in the protoplasm of stimu- 

 lated pseudopodia. Amoeba and leucocytes, as Golubew ('68) and 

 Engelmann ('69) have shown, when acted upon by single induction- 

 shocks, draw in their pseudopodia and assume a spherical shape. 

 The protoplasm of plant-cells, as Klihne ('64) demonstrated in 

 the cells of the stamen-hairs of Tradescantia virginica, is induced 

 likewise to form globules by repeated making and breaking of the 

 constant current or by single induction-shocks (Fig. 203) ; this is 

 also characteristic of naked protoplasm, and can be produced 

 locally by the local application of stimuli. 

 The activity of cilia, as Engelmann (79, 1) and, 

 more recently, Kraft ('90) have observed in 

 ciliated epithelia, is increased to greater 

 rapidity by the galvanic current, the fre- 

 quency and amplitude of the stroke, and 

 hence the useful effect, being especially in- 

 fluenced. In the single flagellum of the 

 flagellate cell also, e.g., in Peranema, the ex- 

 citing effect of the electric current can be 

 observed expressing itself with a single induc- 

 tion-shock by an energetic stroke in the 

 otherwise uniformly rhythmical beat (Fig. 

 204). In the myoids of Infusoria, e.g., in the 

 stalk-myoid of Vorticella, in smooth muscle- 

 cells, and in cross-striated muscle-fibres, ex- 

 citation by a single, brief electrical stimulus, 

 such as a single induction-shock, is expressed 

 by a contraction ; with cross-striated skeletal muscles this can be 

 recorded graphically by means of a myograph (Fig. 205). 



But before bringing to an end the consideration of reactions in 

 contractile substances, the effect of rapidly successive galvanic 

 stimuli deserves attention. The best means of putting a contrac- 

 tile structure into tetanic contraction is afforded by the rhythmic 

 induction-shocks of du Bois-Reymond's sledge-apparatus with the 

 hammer in action. An amoeba or a leucocyte under the in- 

 fluence of rhythmically successive induction-shocks remains in 

 contraction, i.e., preserves its spherical form, as long as the action 

 continues. With the same kind of stimulus muscle likewise is in 

 continual contraction. Muscle here affords a much more favour- 

 able opportunity than with mechanical stimulation to follow the 

 origin of tetanus and to demonstrate the fact that tetanic con- 

 traction consists of discontinuous, single contractions, which follow 



FIG. 204. Peranema, a 

 flagellate infusorian. a, 

 Swimming quietly ; b, 

 stimulated by an induc- 

 tion-shock. 



