XLVIIL] 



ELECTROTONUS. 



243 



over the end of the other, both muscles being in line with each other, and 

 the overlapping portion so arranged that they can be pressed together by 

 means of the small screw-press devised by Kiihne for this purpose. 



Ou stimulating by electrical, chemical, or other stimuli the free end of 

 either muscle, so as to 

 cause that muscle to con- 

 tract, the second muscle 

 also contracts. The nega- 

 tive variation of the 

 muscle-current stimulates 

 the second muscle. This 

 result does not take place 

 if a thin layer of tinfoil 



be placed between the two //// *> \^^^m, ^-^ ->,. T I i ' 



muscles. ""' \W?5i ^\ \ I IP 



9. Biedermann's Modi- 

 fication of Secondary 

 Muscular Contraction. 



If a frog be denuded of its 

 skin and left exposed to 

 the air for twenty-four 



hours the time varying with the temperature, amount of moisture in the air, 

 &c. on causing one muscle to contract, other muscles contract secondarily. 

 On placing the two sartorius muscles in direct contact with each other, when 

 one muscle is made to contract, the other does so secondarily without the use 

 of a muscle-press. 



* 



LESSON XLVIIL 



ELECTROTONUS BLBCTROTONIC VARIATION 

 OF THE EXCITABILITY. 



Electrotonus. When a nerve is traversed by a constant 

 current, its so-called " vital " properties are altered, i.e., its excita- 

 bility, conductivity, and electro-motivity. The region of the 

 nerve affected by the positive pole is said to be in the anelectro- 

 tonic, and that by the negative in the kathelectrotomc condition. 

 Therefore we have to study the 



I. Electro-motive alteration of the excitability and conductivity . 



II. Electro-motive alteration of the electro-motivity. 



1. Electrotonic Variation of the Excitability. 



A. (a.) Connect two small Grove's cells or two Daniell's to a 

 Pohl's commutator with cross-bars (fig. 168), introducing a Du Bois 

 key to short-circuit the battery. From two of the binding screws 

 connect wires with two N.P. electrodes or the platinum electrodes 

 of Du Bois, introducing a short-circuiting key in the electrode 

 circuit (fig. 168). 



