CAUSE OF THE RHYTHMICAL CONTRACTIONS OF THE HEART. 223 



dred years ago, Haller described certain tissues of the body 

 which possessed this "irritability," such as the muscles, 

 stomach, bladder, etc., and the different degrees of irritability 

 with which each one was endowed. 1 He applied this theory 

 to the action of the heart, which he considered as the part 

 endowed with irritability to the highest degree. His theory 

 of the action of the heart was that its rhythmical contraction 

 depended upon the irritability inherent in its muscular fibres. 

 He was far from denying 'the various influences which modi- 

 fied this action, but regarded its actual power of contraction 

 as independent. It will be interesting to review some of the 

 facts which were established by Haller, and by numerous 

 physiologists who have since investigated this subject, and 

 see how far this view of the independence of the contractile 

 power of the heart accords with the present state of our 

 knowledge. 



Experiments have shown that the heart will pulsate for a 

 time when removed from all connection with other parts of 

 the organism. 2 In the cold-blooded animals, in which the 

 irritability of the tissues remains for some time after death, 

 this is particularly marked. It is not the blood in the cavi- 

 ties of the heart which causes it to contract, for it will pul- 

 sate when its cavities have been emptied. It is not the con- 



1 HALLER, Memoires sur la Nature Sensible el Irritable des Parties du Corps 

 Animal, Lausanne, 1756, tome i. These views with regard to the cause of the 

 action of the heart were first advanced by Haller in 1739 in commentaries on the 

 " Institutes " of Boerhaave (Mem. de HALLER, p. 87). 



2 Numerous instances of contractions of the heart in cold-blooded animals con- 

 tinuing for a very long time after excision, are on record. Dr. Dunglison, in his 

 work on Physiology (pp. cit., vol. i., p. 408), mentions several instances where the 

 heart pulsated for from ten to twenty-four hours after removal from the body. 

 The most remarkable examples of this prolonged action were in the heart of the 

 sturgeon. In one instance, in an experiment on a large alligator, we found the heart 

 pulsating, in situ, twenty-eight hours after the animal had been killed by the injec- 

 tion of a solution of woorara. The heart was then excised, and continued to 

 beat during a long series of experiments, until it was arrested by powerful compres- 

 sion with the hand, after it had been filled with water and the vessels tied. 



