224 Mr. Alder son on the 



opinions have been copied, and assented to by every* succeeding 

 physiologist. 



The object of the following remarks, is to shew that their hypo- 

 thesis is not founded on demonstration, nor on sound philosophical 

 principles ; and that it must not be handed down in the same page 

 with that of Harvey, 



We find in a note in John Hunter's Treatise on the Blood, a 

 reason given why the apex of the heart strikes against the chest in 

 its actions, viz., " that the heart throwing the blood into a curved 

 tube, viz. the aorta, that artery at its curve endeavours to throw 

 itself into a straight line to increase its capacity; but the aorta 

 being the fixed point against the back, and the heart in some de- 

 gree loose or pendulous, the influence of its own action is thrown 

 upon itself, and it is tilted forward against the inside of the chest." 

 We are further told in the same note, that " the systole and diastole 

 of the heart simply could not produce such an effect, nor could it 

 have been produced, had it thrown the blood into a straight tube 

 in the direction of the axis of the left ventricle, as in the case with 

 the ventricles of fish, and some other classes of animals." Now 

 this last remark, as far as it relates to the hearts of fish is un- 

 doubtedly true, but it leads to a question which shakes the validity 

 of the former opinion, relative to the motion of the human heart, 

 viz., supposing the aorta in fish to be curved, as the human aorta, 

 the direction of the aortic orifice being still in the axis of the ven- 

 tricle, would the motion of the fish's heart be similar to that of the 

 human heart? It certainly would not; for wliatever re-action 

 might arise from the action of the curve of the artery, this re-action 

 must take place in the direction of the axis, and hence the dis- 

 charge of the blood from the ventricle could only tend to lengthen 

 the ventricle in the direction of the axis. Besides, this action, sup- 

 posing it the effect of the arch of the aorta, must consequently take 

 place after the blood has been expelled from the ventricle by the 



* Barclay on Muscular Motions of Hmnan Bodij, p. 507 ; Richerand's Ele- 

 ments of Physiology, p. 168 ; Mason Good, Study of Medicine, vol. iii. p. 406 j 

 Blumenbach, Institutes of Physiology, Note A, by Dr. Elliolson, p.66;Boslock, 

 Elements of Physiology, p. 31G. 



