86 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



cathodal region, which, as has been said, comes on promptly with 

 strong currents and persists for a time after the current is broken. 



The Opening and the Closing Tetanus. While the du Bois- 

 Reymond law stated above expresses the facts as usually observed 

 upon a nerve-muscle preparation, there are a number of observa- 

 tions which indicate that the excitation at the anode and the 

 cathode during the passages of a current may give rise to a series 

 of stimuli instead of a single stimulus. Thus with sensory nerves 

 it is well known that the stimulation, as judged by the sensations 

 aroused, continues while the current is passing instead of being 

 limited to the moment of making or of breaking of the current. In 

 this respect, as in stimulation by high temperatures, the sensory fibers 

 differ apparently from the motor. When a galvanic current is passed 

 through the ulnar nerve at the elbow sensations are felt during the 

 entire time of passage of the current. But in an ordinary nerve- 

 muscle preparation it is also frequently observed that at the 

 moment of opening the current a tetanic contraction, persisting for 

 some time, is obtained instead of a single twitch. This phenomenon 

 is known as the opening tetanus or Hitter's tetanus, and Pfliiger 

 has shown that the continuous excitation proceeds from the anode, 

 since in the case of a descending current division of the nerve in 

 the intrapolar region brings the muscle to rest. In the same way 

 it frequently happens that upon closing the current through a nerve 

 the muscle, instead of giving a twitch, goes into a persistent tetanic 

 contraction. The tetanus in this case is designated as the closing 

 or Pfliiger 's tetanus. Both of these phenomena are observed 

 especially when the irritability of the nerve is for any reason greater 

 than normal, for instance, when it has been cooled to a low tem- 

 perature. It seems probable, therefore, to many observers that 

 the excitation at the cathode persists in reality during the passage 

 of the current even in motor fibers, although ordinarily the exci- 

 tation makes itself felt upon the muscles only at the moment of 

 closure; the excitations during the passage of the current being 

 either too weak to affect the muscle or the condition of the nerve 

 being such as to prevent their conduction to the muscle. It should 

 be added that the opening and the closing tetanus may be observed 

 also in a muscle when the galvanic current is passed through it. 



Stimulation of the Nerves in Man. For therapeutic as well 

 as diagnostic and experimental purposes it often becomes desirable 

 to stimulate the nerves, particularly the motor nerves, in man. 

 We may use for this purpose either the induced (faradic, alternat- 

 ing) current or the direct battery current (galvanic or continuous 

 current). In such cases the electrodes cannot be applied of course 

 directly to the nerve; it becomes necessary to stimulate through 

 the skin, and the so-called unipolar method is employed. The 



