Chapter II 



The Motions of the Heart as Observed 

 in Animal Experiments 



IN THE first place, when the chest of a living 

 animal is opened, and the capsule surrounding 

 the heart is cut away,^ one may see that the heart 

 alternates in movement and rest. There is a time 

 when it moves, and a time when it is quiet. 



This is more easily seen in the hearts of cold- 

 blooded animals, as toads, snakes, frogs, snails, 

 shell-fish, crustaceans, and fish. It is also more 

 apparent in other animals as the dog and pig, if one 

 carefully observes the heart as it moves more slowly 

 when about to die. The movements then become 

 slower and weaker and the pauses longer, so that it 

 is easy to see what the motion really is and how made. 

 During a pause, the heart is soft, flaccid, exhausted, 

 as in death. 



Three significant features are to be noted in the 

 motion and in the period of movement: 



^ The only reference to the pericardium made by Harvey. The idea 

 that it prevents 6verdistention of the heart probably never occurred 

 to him. For current ideas on the function of the pericardium see 

 J. A, Wilson and W. J. Meek, Amer. J. Physiol., 82: 34 (Sept.) 1927. 



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