110 ELECTRO-PHYSIOLOGY CHAP. 



muscle is repeatedly excited during the stage of relaxation by a 

 short closure of the constant current, its response to the make 

 excitation will generally be less in proportion to the height of 

 its contraction during the previous stimulation. It not infre- 

 quently happens that the muscle, even when fully relaxed, will 

 hardly give any perceptible response to the same stimulus that 

 recently elicited a marked contraction. But in the majority of 

 cases the increment of excitation effects proceeds pari passu with 

 the progressive relaxation of the muscle, so that the twitches 

 served up during the latter period at equal intervals, and of very 

 brief duration, all rise to a uniform height above a line of abscissa 

 corresponding with the descending portion of the curve traced 

 by the muscle after a single excitation. Fick made similar 

 observations with indirect excitation (vid nerve) of a veratrinised 

 frog's muscle (72, p. 146). 



As we have said, the character of the twitches alters in a 

 marked way with rapidly repeated excitation, relaxation soon 

 occurring as quickly as under normal conditions. If the muscle 

 is left for some time unexcited, the first renewed contraction 

 again exhibits all the characteristic veratrin effects. Temperature 

 is an important factor, since the typical contraction-curve of the 

 veratrin muscle is most pronounced at medium temperature, and 

 less characteristic alike in great heat and in cold. In both these 

 cases (Lauder-Brunton and Cash, 73) the phenomena of veratrin 

 contracture disappear, to return again when the cooled or heated 

 muscle is restored to a medium temperature. But the recovery 

 is not invariable, so that it would appear as though the veratrin 

 effect can be permanently abolished by change of temperature. 



Barium, salts act like veratrin upon the substance of striated 

 muscle, while the potassium salts in general act as a muscle 

 poison, depressing excitability more or less quickly, and finally 

 abolishing it. This is to a marked degree the case, even 

 with highly dilute solutions, so that, as indicated by Eanke, 

 the salts of potassium presumably play an important part among 

 the " fatigue products " of muscle. It is certain that both with 

 localised applications of K salts, and on circulating them in 

 solution through the muscle, every characteristic manifestation 

 of muscular fatigue is produced, which can again be entirely 

 cancelled by simply washing out the preparation with 0*6 % 

 NaCl solution. 



