CAUSE OF THE RHYTHMICAL CONTRACTIONS OF THE HEART 221 



lation, and have fallen to the ground, as science has advanced. 

 At the present day, though we are perhaps as far as ever 

 from a knowledge of the actual cause of the regular move- 

 ments, we are pretty well acquainted with the various condi- 

 tions which modify and regulate them, and have arrived at a 

 limit of knowledge which there seems little prospect of ex- 

 ceeding. The enthusiastic dreamers of past ages hoped to 

 discover the seat of the soul and arrive at the principle of 

 life, but we are as much .in the dark as were they with regard 

 to the cause of the various vital phenomena. We know, for 

 example, how to induce contraction in a living muscle, or 

 one which is just separated from the organism and has not 

 yet lost what w r e call its v ital properties ^ but we must confess 

 our utter ignorance when we ask ourselves why it acts 

 in response to a stimulus. The wonderful advances we 

 have made in chemistry and microscopic anatomy do not 

 disclose the vital principle ; and when we come to examine 

 the various conditions under which the heart will continue 

 its contractions, we are arrested by the impossibility of fathom- 

 ing the mystery of the cause of contraction. The heart is, 

 anatomically, very much like the voluntary muscles ; but it 

 has a constant function to perform, and will act without any 

 palpable excitation, while the latter, which have an occa- 

 sional function, act only under the influence of a natural 

 stimulus like the nervous force, or artificial irritation. 

 The movements of the heart are not the only examples of, 

 what seems to be, spontaneous action. The ciliated epithe- 

 lium is in motion from the beginning to the end of life, and 

 will continue for a certain time even after the cells are de- 

 tached from the organism. This motion cannot be explained, 

 unless we call it an explanation to say that it is dependent 

 on vital properties. 



But if we are yet ignorant of the absolute cause of the 

 rhythmical contraction of the heart, we are pretty well ac- 

 qiiainted with the influences which render its action regular, 

 powerful, and sufficient for the purposes of the economy. It 



