106 ELECTRO-PHYSIOLOGY CHAP. 



weak that they only appear in a very slight, but unmistakably 

 rhythmical, tremor of the immersed muscle. Generally, however, 

 these insignificant manifestations are followed at the same, or 

 other, points of the fibre by stronger contractions, with a slower 

 rhythm, which under some conditions cause the muscle to curve 

 round in a semicircle towards the surface or border, or to roll up 

 screw -fashion at regular intervals. For the rest there seems 

 to be an inexhaustible variety in regard to the forms of move- 

 ment, which may be observed in these reactions running parallel 

 to, and interrupting, or not interfering with, each other, but all 

 having in common that at the same point of the muscle, at a 

 given time, there will be uniform rhythm of movement and inci- 

 dence of stimulus. 



It is by no means unusual, especially in the later stages of the 

 action of alkaline salt solutions, to find that for a long time only 

 one point of the immersed muscle continues in rhythmical activity, 

 so that the preparation moves in the same constant rhythm as a 

 beating heart, and this not infrequently gives rise to a phenomenon 

 so strikingly like the " periodic function " of the frog's heart, 

 described by Luciani (70), that the analogy of the two mani- 

 festations is at once apparent. These periods often occur suddenly 

 and quite spontaneously after the preparation has pulsated for a 

 long time in regular rhythm, the regular sequence of beats being 

 interrupted by a longer or shorter interval. In other cases the 

 appearance of the phenomenon is indicated by the fact that after 

 a long series of pulsations of uniform rhythm, the pauses between 

 every pair of beats become gradually longer, without in any way 

 altering the quality of the single contractions. Finally there 

 comes a long pause, and then a new series of pulsations, interrupted 

 again by a period of rest, arid so on. 



At a low temperature the play of rhythmic activity may often 

 be manifested for days. The phenomenon assumes a special 

 interest when it is considered in connection with a series of recent 

 observations by different experimenters upon the ventricle of the 

 frog's heart, detached from the auricle. 



Merunowicz, Kossbach, Stienon, Gaule, Gaskell, Lowit, and 

 others have ascertained that the non-ganglionated " cardiac apex " 

 of the frog may set up regular rhythmical activity when certain 

 chemical substances which supply the nutrition of the preparation 

 are added to a 0*6 % NaCI solution that is intrinsically ineffective. 



