666 DEVELOPMENT AND DISAPPEARANCE OF ELECTROTONUS. 



The persistent moderate shortening of the muscle continued closing contrac- 

 tion (Fig. 194, IV) at times observed during the period of closure of the circuit, 

 is due to the abnormal persistence of the kathodal closing excitation (with strong 

 stimuli in dying muscles, or in the muscles of cooled winter-frogs). Also opening 

 at times gives rise to a similar contraction originating at the anode. Treatment of 

 the muscle with 2 per cent, sodium-chlorid solution containing sodium carbonate 

 increases the permanent contraction considerably, and it appears occasionally as 

 rhythmic shortening. 



If the entire muscle is introduced into the circuit the closing contraction 

 predominates when the current passes in either direction. During the period of 

 closure a permanent contraction is most marked with the ascending current. 



It is a remarkable fact that the constant current has an effect upon a muscle 

 in the state of permanent contraction entirely opposite to that upon a relaxed 

 muscle. If a constant current be passed, by means of unpolarizable electrodes, 

 longitudinally through a muscle in a state of permanent contraction, for example 

 as a result of poisoning with veratrin, or through the contracted ventricle, relaxa- 

 tion begins on closure at the anode and extends thence. On opening the current 

 in the permanently contracted muscle the relaxation takes place from the kathode. 



In correspondence with these remarkable phenomena, the currents in the 

 muscular substance appear in accordance with the law that every contracted 

 portion is negative with relation to every resting portion of a muscle. Perhaps 

 the experiments of Pawlow throw light upon these observations. This observer 

 found that the sphincters of mussels contain nerve-fibers, irritation of which 

 causes the production in the muscle of a state of relaxation. 



If a nerve or muscle has been traversed for a considerable time by 

 a constant current, permanent tetanus often appears after the opening 

 so-called Ritter's opening tetanus. This is abolished by closing a 

 current passing in the original direction, while the closing of a current 

 in the opposite direction increases it Volta's alternative. The per- 

 sistent passage of the current increases the irritability for the opening 

 of a current in the same direction and for the closing of a current in the 

 opposite direction; while, conversely, it diminishes the irritability for 

 the closing of a current in the same direction and the opening of a current 

 in the opposite direction. 



According to Grutzner, Tigerstedt, and others, the cause for the opening 

 contraction resides in part in the development of polarizing after-currents. The 

 irritating effect of the kathode is dependent upon the escape of water at this 

 point. Engelmann and Grunhagen explained the opening and closing tetanus in 

 a different manner, namely as due to latent stimulation of the prepared 

 nerve, as a result of drying and fluctuations in temperature, the stimuli being 

 in themselves too feeble to cause tetanus, but becoming effective when increased 

 irritability of the nerve is set up in the vicinity of the kathode after closing, in 

 that of the anode after opening. 



Biedermann showed that under certain circumstances two opening contrac- 

 tions could be observed in succession in the frog-nerve-preparation, of which the 

 second or later corresponds to Ritter's tetanus. The first of these contractions is 

 caused by the disappearance of anelectrotonus in the sense of Pniiger. The 

 second is to be explained like Ritter's opening tetanus in the sense of Engelmann 

 and Grunhagen. 



Pathological. The observation is rarely made in morbid conditions o the 

 nervous system (hysteria) that after interruption of an electrical current through 

 a nerve, tetanic contractions persist, and this has been appropriately designated 

 the neurotonic reaction. 



Simultaneous Action of the Constant Current and the Inherent Current. The 

 Action of Two Currents. In the frog-preparation arranged for testing the con- 

 traction-law, a demarcation-current naturally occurs in the nerve. If a feeble, 

 artificial, stimulating current be applied to such a nerve interference-phenomena 

 may occur between these two currents. The closing of an exceedingly feeble 

 constant current causes a contraction that is really no closing contraction, but 

 is due to opening (conduction) of a branch of the demarcation-current. Con- 

 versely, the opening of an exceedingly feeble constant current may cause a con- 



