Motion of the Heart. 



22t 



contraction of its parietes. Now we need scarcely seek the autho- 

 rity of Laennec*, to convince us that the impulse of the heart is 

 only felt at the moment of the systole of the ventricles, and hence the 

 heart must have already commenced its motion towards the pa- 

 rietes of the chest, previously to the blood's arriving at the arch 

 of the aorta. The heart's motion must therefore depend on other 

 causes than the efforts of this great vessel t. 



As the language of the schools is not familiar to all, and as we 

 sometimes find that an appeal to some effect that is tangible often 

 renders, or appears to render, a fact more clear and more easy to 

 be understood, than the strictest mathematical reasoning, I may be 

 excused annexing a sketch of that beautiful and well known in- 

 vention of Mr. Barker, called Barker's Mill. 



• V AmeuUalion Midiale, p. 207, v. ii. 



t It is clear from the following passage, that Laennec was aware of tlie fact 



