302 FEATURES OF CARDIAC CONTRACTION. [BOOK i. 



frog, will beat spontaneously with great ease and for a long time 

 when isolated from the auricles. Further, a mere strip of this 

 ventricular muscular tissue if kept gently extended, and continually 

 moistened with blood or other suitable fluid, will continue to beat 

 spontaneously with very great regularity for hours or even days, 

 especially if the series be started by the preliminary application 

 of induction shocks rhythmically repeated. 



In connection with this question we may call attention to the 

 fact that the cardiac muscular fibre is not wholly like the skeletal 

 muscular fibre; in many respects the contraction or beat of the 

 former is in its very nature different from the contraction of the 

 latter ; the former cannot be considered like the latter a mere 

 instrument in the hands of the motor nerve fibre. The features 

 of the beat or contraction of cardiac muscle may be studied on 

 the isolated and quiescent ventricle, or part of the ventricle of the 

 frog. When such a ventricle is stimulated by a single stimulus, 

 such as a single induction shock or a single touch with a blunt 

 needle, a beat may or may not result. If it follows it resembles, 

 in all its general features at least, a spontaneous beat. Between 

 the application of the stimulus and the first appearance of any 

 contraction is a very long latent period, varying according to 

 circumstances, but in a vigorous fresh frog's ventricle being about 

 "3 sec. The beat itself lasts a variable but considerable time, 

 rising slowly to a maximum and declining slowly again. Of 

 course when the beat of the whole ventricle is recorded by one or 

 other of the methods given in 154, what the tracing really 

 shews is one of the results of the contraction of the cardiac 

 fibres, and gives, in an indirect manner only, the extent of the 

 contraction of the fibres themselves. We may however study in 

 a more direct way the contraction of a few fibres by taking a 

 slip of the ventricle (and for this purpose the tortoise is preferable 

 to the frog) and suspending it to a lever after the fashion of a 

 muscle-nerve preparation. We then get upon stimulation a curve 

 of contraction, characterised by a long latent period, a slow, long- 

 continued rise, and a slow, long-continued fall, a contraction in 

 fact more like that of plain muscular tissue than of skeletal 

 muscular tissue. In the tortoise the contraction is particularly 

 long, the contraction of even the skeletal muscles being long 

 in that animal ; it is less long, but still long in the frog, shorter 

 still, but yet long as compared with that of the skeletal muscles, 

 in the mammal. 



The beat of the ventricle then is a single but relatively slow 

 prolonged contraction wave sweeping over the peculiar cardiac 

 muscle-cell, passing from cell to cell along the fibre, from fibre to 

 fibre along the bundle, and from bundle to bundle over the 

 labyrinth of the ventricular walls. 



Like the case of the skeletal muscle, this single contraction 

 is accompanied by an electric change, a current of action. The 



