Motion of the Heart. 227 



Let us suppose the annexed figure to represent* the left ventricle 

 a a, the aortic orifice w n, a normal to that orifice/ Now when the 

 ventricles are filled just prior to their contraction, (the auricles of 

 course being empty) the aortic orifice will at this time be situated 

 posteriorly, and to the right side of the ventricle, and hence the 

 normal n n, from the centre of the orifice, will intersect the parietes 

 in a point (n,) situated anteriorly, and to the left side of the ven- 

 tricle. Hence a vertical plane passing through {n n), (the body 

 lying'horizontally, and the heart in its natural place) will nearly 

 be in the direction of the heart's motion. 



Let us further suppose the aortic orifice a a to be closed by a 

 plug, retained in its place by the finger, and that the ventricle be 

 now allowed to contract ; it is clear, that it will require a certain 

 force to keep the plug in its place, i. e. to counteract the effect of the 

 re-action of the blood arising from the contraction which takes 

 place in a similar t portion of the parietes on the opposite side of 

 the ventricle in a contrary direction. 



If then, we remove the finger, and allow the blood to escape, the 

 re-action on the opposite side of the ventricle remains uncounter- 

 acted ; and it is by this uncounteracted force that the heart is 

 moved. 



That the arch of the aorta may modify the heart's motion, I will 

 not deny, but that the heart would have this motion independently 

 of the aorta altogether, so long as the aortic orifice be out of the 

 axis of the ventricle, is most certainly true. 



I am aware that mechanical physiologists are in no great repute 

 at present, and probably no organ has contributed more to produce 

 this opinion than the heart itself ; still it must be admitted, that % 



* The whole effect produced does not arise from the action of the left ven- 

 tricle alone, nor will the heart's motion be in the direction nn, but in that of 

 the resultant of the two forces produced by the contraction of the left and right 

 ventricle conjointly; for our purpose, the consideration of the left ventricle 

 will be sufficient. 



t We here suppose, for sake of convenience, that each portion of the parietes 

 of the ventricle contracts with an equal force. 



t Bostock, Ekmeniary Treatise on Phymlogy, vol. i. p. 41C. 



