STIMULI AND THEIR ACTIONS 



425 



between the individual stimuli to be recognised clearly (Fig. 207, 

 II). If induction-shocks be allowed to act upon the muscle in 

 more rapid succession, as they are produced in the secondary coil 

 by the play of Neef 's hammer, the effect of each single shock is no 

 longer to be distinguished as such, but a smooth curve results, 

 which rises rather steeply and then, if the stimulation be not con- 

 tinued too long, maintains itself at a uniform height as a straight 

 line (Fig. 207, III). Thus, by increasing the rate of succession of 

 the stimuli, it is possible to follow the formation of complete 

 tetanus from the completely finished single contractions through 

 all the transition-forms of incomplete tetanus, and thereby to 

 afford the proof that, in reality, tetanus is a discontinuous cori- 



FIG. 206. Muscle-writer. The nerve-muscle preparation is fixed in the muscle-holder ; the nerve 

 is stimulated by pointed platinum electrodes ; and the muscle records its movement upon a 

 rotating, blackened drum by means of a writing-lever. 



traction. All continued contractions that are performed in the 

 human body under nervous influence are, like tetanus artificially 

 produced, discontinuous phenomena composed of many single 

 contractions following one another in rapid succession. 



It should be mentioned that there are forms of living substance 

 that are not influenced at all by induction-shocks, either by 

 single ones or by shocks succeeding one another rapidly or slowly, 

 however strong they may be. Such objects are Orbitolites, 

 Amphistegina, and other marine Rhizopoda. Their protoplasm 

 requires for reaction a longer duration of the stimulus than the 

 lightning-like induction-shock possesses. 1 



As regards other excitation-effects of galvanic stimulation, 

 mechanical motile effects are produced, not only in contractile 



1 Of. Verworn ('92, 2). 



