652 CURRENTS OF STIMULATED MUSCLES AND NERVES. 



CURRENTS OF STIMULATED MUSCLES AND NERVES AND OF 

 SECRETORY ORGANS. 



1. If a muscle that exhibits a strong electrical current is thrown 

 into tetanic contraction, best by means of tetanization of its nerve, its 

 current is enfeebled, at times even to the point of complete return of the 

 magnetic needle to zero This phenomenon is the negative variation. 

 It is directly proportional to the primary deflection of the magnetic 

 needle and to the energy of the contraction of the muscle. 



After the tetanus the muscle-current is feebler than before. If the muscle 

 be placed upon the electrodes in such a manner that the current is a feeble one, 

 a diminution of this feeble current appears during tetanus in an analogous manner. 

 In the ineffective arrangement the contraction of the muscle has no influence 

 upon the magnetic needle. If the contraction of the muscle is prevented by 

 making it tense, a somewhat slighter negative variation is observed. Therefore, 

 it is also smaller in the isometric than in the isotonic act. If a contracted muscle 

 be stretched, the negative variation present decreases. If, however, a resting 

 muscle be stretched the resting current is diminished. 



2. Excised frog-muscles thrown into a state of tetanus through their 

 nerves exhibit electromotive force, action-current. A descending current 

 is present, for example, in the tetanized gastrocnemius of the frog and 

 a similar current in the entire hind leg. In wholly intact muscles of 

 man, however, thrown into tetanic contraction through their nerves, such 

 a current is wanting. Also wholly intact frog's muscles directly thrown 

 into tetanus exhibit no current. 



3. If a muscle is momentarily irritated directly at one extremity, 

 so that the contraction-wave rapidly traverses the entire length of the 

 muscle-fibers, every part of the muscle is successively negative elec- 

 trically shortly before it undergoes contraction. A wave of negativity 

 thus precedes the wave of contraction. The former therefore occurs 

 during the period of latent irritation. Waves of negativity and con- 

 traction have the same velocity of about 3 meters in a second. The 

 negativity, which at first increases and then diminishes, continues at 

 each point for only about 0.003 second. 



4. Also a single contraction indicates the development of an elec- 

 trical current in the muscle. The pulsating frog's heart serves as an 

 appropriate illustration, the observation being made with the aid of the 

 electrogalvanometer. Each pulsation causes a deflection of the needle of 

 the instrument, and this takes place earlier than the contraction of the 

 heart-muscle itself. The electrical process in the muscle causing the nega- 

 tive variation precedes in general the contraction, and occurs, therefore, 

 in the stage of latency. In the contraction of the wholly intact gastroc- 

 nemius muscle of the frog stimulated through its nerve there is at first 

 a descending and then an ascending current. 



Careful investigations of the electrical processes in the pulsating heart have 

 shown that, with the cardiac pulsation, first the base and then the apex of the 

 ventricle becomes negative. A brief latent period occurs in advance. If the 

 heart-muscle is placed in a condition of relaxation by irritation of the vagus, a 

 positive variation is naturally observed in the muscle-current. On the other 

 hand, irritation of the accelerator nerve in the condition of arrest due to muscarin, 

 even when the pulsation of the heart is not stimulated anew, gives rise to negative 

 variation. 



Also in man an electrocardiogram can be obtained if the two hands are con- 

 nected with the capillary electrometer. The right arm exhibits the electrical 



