CURRENTS OF STIMULATED MUSCLES AND NERVES. 653 



tension of the base of the heart, the left arm that of the apex. In correspondence 

 with the different individual phases of a cycle of the heart the electrocardio- 

 gram is complicated. Five variations appear in the course of the contraction: 

 The first, third, and fifth indicate negativity of the base of the heart, the second 

 and fourth negativity of the apex. Also the two muscles of the iris exhibit nega- 

 tive variation in their contraction. Naturally, the descending contraction-wave 

 in the esophagus observed in the act of swallowing is attended with correspond- 

 ing electrical phenomena. 



The electrical processes in muscle on simple contraction are exhibited also 

 by the frog-preparation. If a segment of the nerve of such a preparation be 

 placed upon a muscle the frog-preparation twitches whenever the muscle is made 

 to contract. If the nerve of a frog-preparation is placed upon a pulsating mam- 

 malian heart, a contraction takes place in the leg with every pulsation. Thus, 

 after division of the phrenic nerve, particularly on the left side, the diaphragm 

 contracts synchronously with the heart-beat. This contraction is designated the 

 secondary contraction. The moving muscle thus stimulates another muscle applied 

 to it. This phenomenon occurs readily if the muscles employed are in a state of 

 beginning desiccation. 



A muscle in a state of tetanic contraction from the action of an induced 

 current causes secondary tetanus in a frog-preparation in contact with the muscle. 

 The latter is considered an evidence that in the process of negative variation in 

 the muscle many current-variations occurring in rapid succession must have teen 

 present, as only rapid variations of this kind have a tetanizing effect upon the 

 nerve, and not long-continued current-variations. 



Also when the muscle is in a state of tetanic contraction (toad) as a result of 

 voluntary innervation, or of chemical irritation, or of strychnin-poisoning, second- 

 ary tetanus generally does not take place in an applied frog-preparation, although 

 Loven has observed secondary strychnin-tetanus, comprised of from 6 to 9 con- 

 tractions in a second. Lippmann's sensitive capillary electrometer (Fig. 229) 

 also shows that both strychnin-spasm, as well as the voluntary contraction, are 

 discontinuous processes. The slight activity of chemical irritants is explained by 

 the fact that they do not cause the muscle-fibers to enter promptly into a state of 

 uniform contraction. In case of voluntary tetanus and strychnin-tetanus the 

 electrical process takes place perhaps with insufficient variation in the current. 

 For this reason also muscles in a state of tetanic contraction in the normal bcdy 

 do not stimulate adjacent nerves or muscles. 



Biedermann made the remarkable observation that striated muscle under 

 the influence of ether-vapor is thrown into a state in which on irritation it 

 exhibits no appreciable alteration of form or movement, while, on the other 

 hand, changes demonstrable with the aid of the galvanometer appear at the point 

 of irritation in the same degree as prior to the action of the ether, as an expression 

 of the irritation, but in consequence of the abolished power of conduction they 

 are capable of manifesting themselves only locally. 



5. If a nerve resting with its transverse section and surface upon the 

 electrodes be irritated electrically, chemically, or mechanically (or 

 also, if this be possible, reflexly), its current diminishes. This 

 negative variation, which may be propagated in both directions in 

 the nerve, is made up of periodic interruptions of the original current 

 occurring in rapid succession, as in the contracted muscle. Hering 

 was able by this means, as in the muscle, to induce secondary contrac- 

 tion or secondary tetanus. The extent of the negative variation is de- 

 pendent upon the extent of the primary deflection, upon the degree of 

 irritability of the nerve and upon the strength of the irritant applied. 

 The negative variation is demonstrable both on tetanizing with indi- 

 vidual waves of irritation. The negative variation has not yet been 

 observed in wholly intact nerves. 



Hering found that the negative variation of the nerve-current induced by 

 electrical tetanization is followed in general by a positive variation. It increases 

 to a certain degree with the duration of the irritation, with the strength of the 

 stimulating currents with commencing desiccation of the nerves, and if the point 



