IX 



CAEDIAC MUSCLE AND NEKVES 



319 



certain inertia in the heart, associated with exaggeration of tonus, 

 and that the electrical stimuli arouse the heart from this state, 

 when it gradually recovers its activity, systolic as well as diastolic 

 (Fig. 141). 



With regard to the tonicity of cardiac muscle, i.e. the inter- 

 mediate state between systole and diastole, at the pause, Fano 

 discovered an interesting phenomenon on the heart of the tortoise 

 (Emys europea). If one auricle of this animal is connected by a 

 thread with a writing lever, its spontaneous beats complete them- 



FIG. 142. A and B, Myograms from auricle of tortoise heart (Emys europea), obtained by sus- 

 pension method ; showing two different .forms of rhythmical oscillation of auricular tone. 

 (Fano.) 



selves above a line of rhythmical oscillating tonicity. These 

 automatic oscillations of tone in the auricle are of varying 

 intensity, and comprise a larger or smaller number of beats (Fig. 

 142, A and B). If the rhythm of the two auricles is recorded 

 simultaneously, it will be seen that while the beats are perfectly 

 synchronous, the oscillations in tone of the two auricles are quite 

 independent as regards intensity and frequency. When the heart 

 is exhausted the oscillations in tone are the first to disappear. On 

 c 



C, Oscillations of auricular tone in toad's heart (Bufo virldis) (Bottazzi). 

 D, The same from heart of Rana esculenta. 



exciting the vagi, the tonic oscillations increase, while the beats 

 are arrested. These facts led Fano to suggest that the rhythm of 

 tonicity may be due to the contraction and expansion of a proto- 

 plasmic substance, other than that which determines the rhythm 

 of the beats. 



Bottazzi observed automatic oscillations in tonus both in the 

 auricles of the amphibian heart (Fig. 142, C and D) and also on 

 the sinus venosus, even when they were bloodless. Since he found 

 the same phenomenon in the oesophagus of amphibia and of the 

 chick embryo, and Ducceschi has noted it in the stomach of the 

 dog (organs which consist of muscle cells that are very rich in 



