CHAPTER XV. 

 THE WORKING OF THE HEART AND BLOOD-VESSELS. 



The Beat of the Heart. It is possible by methods known 

 to physiologists to open the chest of a living animal, such 

 as a rabbit, made insensible by chloroform, and see its 

 heart at work, alternately contracting and diminishing the 

 cavities within it, and relaxing and expanding them. It is 

 then observed that each beat commences at the mouths of 

 the veins which open into the auricles; and from there runs 

 over the rest of the auricles, and then over the ventricles; 

 the auricles beginning to dilate the moment the ventricles 

 start their contraction. Having finished their contraction, 

 the ventricles begin to dilate, and then for some time 

 neither they nor the auricles are contracting, but the 

 whole heart is expanding. The contraction of any part of 

 the heart is known as its sys'to-le, and the relaxation as its 

 di-as'to-le, and since the two sides of the heart work syn- 

 chronously, the auricles together and the ventricles to- 

 gether, we may describe a whole " cardiac period " or 

 "heart-beat" as made up successively of auricular systole, 

 ventricular systole, and pause. In the pause the heart, if 

 taken between the finger and thumb feels soft and flabby, 



What is seen when the beating heart of a living animal is exposed? 

 When do the auricles begin to dilate? What is the state of the heart 

 for a short time after the end of a ventricular contraction? What is 

 meant by the systole of apart of the heart? What by the diastole? Of 

 what does a cardiac period consist? How does the heart feel to the 

 touch during the pause? 



[216] 



