BY DR. MICHAEL FOSTER. 395 



The exciting current being made, a negative variation sweeps 

 over A and is gone. There remains, however the anelectrotonic 

 increase of the natural current of A along the whole region from 

 the positive pole to the free end. Now let fall B as directed. 

 A contraction in the muscle of B will follow. 



This can only be due to the electro ton ically increased natural 

 nerve current of A acting as a stimulus to the nerve of B when 

 the circuit is closed by a portion of B, and so causing a nervous 

 impulse just as the closing of any other galvanic current 

 would. 



And inasmuch as the electric intensity of the electrotonic 

 increase (or decrease) is much greater than that of the negative 

 variation, the secondary contractions in the Obs. I., II., III. 

 are chiefly due to this cause. 



CHAPTER XXX. 



VARIOUS FORMS OF STIMULATION OF MUSCLE AND 

 NERVE. 



I. Mechanical Stimulation. A blow, sufficiently strong 

 and sudden, applied to either muscle or nerve, .will produce a 

 contraction; and a series of such blows repeated sufficient^ 

 rapidly will produce a tetanus. 



This may be roughly shown by striking simply by hand, 

 with some thin but blunt instrument, either muscle or nerve. 



For more exact purposes, the tetanomotor of Heidenhain may 

 be used, and can be applied equally to muscle or nerve. For a 

 description, sec Rosenthal, Electricitatslehre, p. 116. 



A simpler method is that of Mare} T 's, with a tuning-fork. 



06s. I. Get ready a nerve-muscle preparation. Place the 

 nerve on a small piece of India-rubber sheeting stretched quite 

 tight over a ring of wood or metal. The object of the elastic 

 India-rubber is to soften the violence of the blows given. Ar- 

 range a tuning-fork on a stand, in such a position that the 

 vibrations of the tuning-fork shall take place at right angles to 

 the nerve. Set the fork going, and bring it in slight contact 

 with the nerve. The muscle will at once be thrown into teta- 

 nus, which may be recorded on the cylinder. 



O6.s. II. A muscle (gastrocnemius, or, better, one of the recti) 

 of a frog poisoned with urari, may be placed on the caoutchouc 

 in place of the nerve. 



Tetanus will be then obtained by direct mechanical irritation 

 of the muscle itself, without intervention of the nerves. 



