570 rittek's opening tetanus. 



parts; on opening the current applied to muscle in continued contraction, the 

 relaxation proceeds from the cathode. 



Corresponding to this remarkable phenomenon, Biedermann found as regards the currents 

 in the muscle-substance following the ordinary law, that every contracted part is negative to 

 troy passive section of the muscle. Perhaps the experiment of Pawlow, who found nerve-fibres 

 in the adductor muscle of the mussel, whose stimulation caused relaxation of the muscular 

 contraction, may throw some light on this question. 



Bitters Opening Tetanus. If a nerve or muscle be traversed by a constant 

 current for some time, we often obtain a prolonged tetanus, after opening the 

 current (Ritter's opening tetanus, 1798). It is set aside by closing the original 

 current, while closing a current in the opposite direction increases it ("Volta's 

 alternative "). The continued passage of the current increases the excitability for 

 the opening of the current in the same direction, and for the closing of the reverse 

 current ; conversely, it diminishes it for the closing of the current in the same 

 direction, and for the opening of the reverse current (Volta). 



According to Griitzner and Tigerstedt, the cause of the opening contraction is partly due to 

 the occurrence of polarising after-currents ( 333), and according to Hermann to a diminution 

 of the anodic positive polarisation. 



Engelmann and Griinhagen explain the occurrence of opening and closing tetanus, thus, as 

 due to latent stimulations, drying, variations of the temperature of the prepared nerve, which of 

 themselves are too feeble to cause tetanus, but which become effective if an increased excitability 

 obtains at the cathode after closure, and at the anode after opening the current. 



Biedermann showed that, under certain conditions, two successive opening contractions can 

 be obtained in a frog's nerve-muscle preparation, the second and later one corresponding to 

 Ritter's tetanus. The first of these contractions is due to the disappearance of anelectrotonus 

 in Pfliiger's sense ; the second is explained, like Ritter's opening tetanus, in Engelmann and 

 Griinhagen'a sense. 



Simultaneous action of the constant current and the nerve-current. Action of two currents. 

 In ;i nerve-muscle preparation used to prove the law of contraction, of course a demarcation- 

 current is developed in the nerve ( 334, II.). If an artificial weak stimulating-current be 

 applied to such a nerve, we obtain an interference effect due to these two currents ; closing a 

 weak constant current causes a contraction, which, however, is not properly a closing contrac- 

 tion, but depends upon the opening (or derivation) of a branch of the demarcation-current ; 

 conversely, the opening of a weak constant current may excite a contraction, which is really due 

 to the closing of a side branch of the nerve-current, in a secondary circuit through the electrodes 

 (Hcring, Biedermann, Griitzner). 



If two induction shocks be simultaneously applied to a motor nerve, two cases are possible. 

 Either the one shock is so feeble that the nerve is not thereby sufficiently excited to cause a 

 contraction, while the other shock causes only a feeble contraction. In this case, the sub- 

 raaximal shock plays the part of a weak constant current, and the size of the contraction 

 depends only upon whether the effective stimulus was applied in the area of the anode or the 

 cathode of the submaximal shock (Sewall, Griinhagen, Wcrigo). If, however, unequal, strong, 

 induction shocks, each of which is effective but separated from each other on account of 

 the electrotonic action be applied to a nerve, then the result is as if the stronger alone was 

 active. The feebler wave of excitation passes completely into the stronger one {Griinhagen, 

 Wcrigo). 



337. TRANSMISSION OF NERVOUS IMPULSES. 1. If a motor nerve 

 be stimulated at its central end (1) a condition of excitation is set up, and (2) 

 an impulse is transmitted along the nerve to the muscle with a certain velocity. 

 The latter depends on the former and represents the function of conductivity. 

 The velocity is about 27J metres [about 90 feet] per second (v. Ilelmholtz), and for 

 the human motor nerves 33*9 [100 to 120 feet per second] (v. Ilelmholtz and Baxt). 



The velocity is less in the visceral nerves, e.g., in the pharyngeal branches of the vagus 8*2 

 metres [26 feet] (Chauveau)-, in the motor nerves of the lobster 6 metres [18 feet] {Fredtricq and 

 van de Velde). 



Modifying Conditions. The velocity is influenced by various conditions : 

 Temperature. It is lessened considerably by cold (v. Ilelmholtz), but both high 

 and low temperatures of the nerve (above or below 15 to 25 C.) lessen it (Steiner 

 and Trojtzky) ; also curara, the electrotonic condition (v. Bezold) ; or only anelectro- 

 tonus, while cathelectrotonus increases it (Rutherford, Wundt). It varies also with 



