DEVELOPMENT AND DISAPPEARANCE OF ELECTROTONUS. 663 



passing the irritating current simultaneously through the path of the polarizing 

 current. 



Testing Electrotonus in Inhibitory Nerves. In order to ascertain the action 

 of the cardioinhibitory vagus fibers in electrotonus Landois proceeded as follows: 

 If dyspnea be excited in rabbits, the number of heart-beats diminishes because the 

 dyspneic state of the blood irritates the cardioinhibitory center in the medulla 

 oblongata. If, under such conditions, a constant descending current applied to 

 the vagus is closed, the nerve of the opposite side having been previously divided, 

 the number of pulse-beats again increases descending extrapolar anelectrotonus. 

 If, on the other hand, the current is sent through the nerve in an ascending direc- 

 tion, the number of heart-beats diminishes still further with feeble currents, while 

 with strong currents the number increases ascending extrapolar katelectrotonus. 

 From the foregoing it appears that the action of the inhibitory nerves in electro- 

 tonus is exactly the opposite of that of the motor nerves. 



Testing Electrotonus in Sensory Nerves. In a decapitated frog the sciatic 

 nerve on one side is dissected free and isolated. If the nerve be irritated at one 

 point with sodium chlorid reflex contractions take place in the other leg through 

 the intact spinal cord. These disappear as soon as a constant current is closed 

 on the nerve in such a manner that the salt is situated in the anelectrotonic 

 segment. 



Testing Electrotonus in Nerves of Special Sense. Katelectrotonus at the 

 central extremity increases the irritability in all nerves of special sense, 

 in greatest degree in the eye for the shortest light -waves, on the tongue for acid 

 taste. Anelectrotonus at the central extremity diminishes the electrical irrita- 

 bility, in the eye in least degree for the longest waves; at the tip of the tongue 

 there develops a salty taste, on the posterior portion a bitter taste. At the 

 moment of closure or of opening there occur alone in the eye and the ear so- 

 called flashes. These result, however, only when muscular contractions take 

 place at the same time. They are, therefore, caused in the eye solely by sudden 

 movement of the eyeball, and in the ear by that of the muscles of the auditory 

 ossicles, which are suddenly contracted strongly. 



In the muscle the intrapolar segment is in a state of altered irritability 

 during electrotonus. Also the delay in conduction extends only to this 

 area. 



To the question as to the real nature of the galvanic effects Loeb 

 replies that probably all electrical effects upon living tissues are only 

 indirect, that those effects that 'are designated electrical are in reality 

 only the chemical and molecular effects of the ions or the combinations 

 formed by them. 



THE DEVELOPMENT AND THE DISAPPEARANCE OF ELECTRO- 

 TONUS. 



THE LAW OF CONTRACTION. THE LAW OF POLAR STIMULATION. 



Both at the moment of development and at that of disappearance 

 of electrotonus, therefore on closing and on opening the circuit, the 

 nerve undergoes irritation, i. On closing the circuit, this stimulation 

 occurs only at the kathode, at the moment when katelectrotonus de- 

 velops. 2. On opening the current, the stimulation takes place only at 

 the anode, at the moment when anelectrotonus disappears. 3. Of 

 these two stimuli that attending the development of katelectrotonus 

 is stronger than that caused by the disappearance of anelectrotonus. 



That the stimulation on opening the current occurs at the anode was dem- 

 onstrated by Pniiger in the following manner with the aid of Ritter's opening- 

 tetanus. The latter consists in the development of tetanus of some duration 

 after the opening when a strong constant current is passed through a nerve- 

 segment of considerable length. If the current is a descending one, this tetanus 

 ceases immediately on division of the intrapolar nerve-segment, an evidence that 



