166 ELECTRO-PHYSIOLOGY 



considerable augmentation in the height of the closure twitches. 

 At a later stage the closure of even weak currents causes tetanic 

 shortening of the muscle. The opening twitch then appears along 

 with the closing contraction. The direction in which this first 

 occurs depends less upon direction of current than upon what 

 point of the tract of nerve between the two electrodes is sub- 

 mitted first, and in a higher degree, to the influence of dehydration. 

 If the electrodes are applied to an undivided nerve, so that the 

 sacral plexus falls for the greater part within the region of the 

 upper electrode, the opening excitation will be seen, on account 

 of the slow drying of this the thickest portion of the nerve, to 

 appear first with ascending direction of current ; while, if the elec- 

 trodes are placed in the middle of the nerve, the break twitch follows 

 almost simultaneously upon the strengthened make twitch, with 

 both directions of current, unless one or the other part of the nerve 

 is protected from loss of water by frequent moistening with 0'6 / Q 

 NaCl. If the excitation is limited to weak currents, the closure 

 lasting only so long as to produce a visible opening excitation 

 (a few seconds is, as a rule, sufficient), there will regularly be a 

 more or less delayed appearance of the opening twitch, the 

 magnitude of which depends to a high degree upon the duration 

 of closure of the current. If this is very brief, the break twitch 

 may fail altogether, even when the excitability of the nerve is 

 considerably increased, while a vigorous twitch never fails to 

 appear when the current remains closed a little longer. It is 

 remarkable that the form of the curve also depends essentially 

 upon the duration of current, every transition existing between 

 a simple muscular contraction, which cannot be distinguished 

 from the closure twitch, and a long-sustained tetanic shortening 

 (Bitter's opening tetanus). 



That this opening tetanus, which readily appears at an 

 advanced stage of desiccation, after a brief closure of weak 

 currents, must be regarded as homologous with the opening 

 twitch of earlier stages, inasmuch as both are due to the same 

 causes (to be described below), is evident both from the presence 

 of the above-described transitional forms, and from the fact that 

 the opening tetanus makes the same retarded entrance as the 

 opening twitch. 



Pfliiger (2, p. 75) was the first to draw attention to this 

 significant fact in relation to the opening twitch. He observed 



