RHYTHM AN INHERENT PROPERTY OF HEART MUSCLE 103 



There are several conclusions to be inferred from such experiments. 



A. The excised heart beats rhythmically. Therefore the rhythm is 

 not dependent upon external rhythmic stimuli reaching it via its 

 nerves, but is due to some intrinsic source possessing a rhythmic 

 activity. There are two possibilities, (a) The rhythmic activity 

 may be an inherent property of the muscle fibres, (b) The heart 

 contains in itself nerve cells and nerve fibres ; and the rhythm may 

 be a characteristic of some of these cells. By this experiment taken 

 alone we are not able to prove which of these two possibilities is the 

 correct one. The last part of the experiment, if it succeed, is the most 

 helpful in deciding, but the frog's heart is not a very suitable subject 

 to employ for this particular purpose. On a tortoise heart Gaskell has 

 shown that the apex, which examination proves to be free from nerve 

 cells, can be taught to beat rhythmically. Further facts tending 

 to prove that the rhythm is inherent in the muscle cells are : 

 (i.) the heart beats rhythmically in embryonic life, while it is still of 

 tubular form and before it has gained any nervous connection with the 

 central nervous system ; (ii.) nicotine has been proved to paralyse nerve 

 cells, but a heart poisoned with nicotine continues to beat rhythmi- 

 cally ; (iii.) there is no difficulty in ascribing the rhythm to the heart 

 muscle, for cross-striated muscle may be caused to contract rhythmi- 

 cally by immersing it, under proper tension, in Biedermann's fluid, ' 

 and the bulbus arteriosus, which contains no ganglion cells, beats 



1 Biedermann's fluid is made by dissolving 5.g. NaCl, 2.g. Na H,P0 4 and 0'59.g. 

 Na.,CO., in 1 litre of water. 



