82 WILLIAM HARVEY 



when it moves, becomes of a paler color, when quiescent of 

 a deeper blood-red color. 



From these particulars it appears evident to me that the 

 motion of the heart consists in a certain universal tension 

 both contraction in the line of its fibres, and constriction in 

 every sense. It becomes erect, hard, and of diminished size 

 during its action; the motion is plainly of the same nature 

 as that of the muscles when they contract in the line of their 

 sinews and fibres; for the muscles, when in action, acquire 

 vigor and tenseness, and from soft become hard, prominent, 

 and thickened: and in the same manner the heart. 



We are therefore authorized to conclude that the heart, 

 at the moment of its action, is at once constricted on all 

 sides, rendered thicker in its parietes and smaller in its 

 ventricles, and so made apt to project or expel its charge 

 of blood. This, indeed, is made sufficiently manifest by the 

 preceding fourth observation in which we have seen that 

 the heart, by squeezing out the blood that it contains, 

 becomes paler, and then when it sinks into repose and the 

 ventricle is filled anew with blood, that the deeper crimson 

 colour returns. But no one need remain in doubt of the 

 fact, for if the ventricle be pierced the blood will be seen 

 to be forcibly projected outwards upon each motion or pul- 

 sation when the heart is tense. 



These things, therefore, happen together or at the same 

 instant: the tension of the heart, the pulse of its apex, which 

 is felt externally by its striking against the chest, the thick- 

 ening of its parietes, and the forcible expulsion of the blood 

 it contains by the constriction of its ventricles. 



Hence the very opposite of the opinions commonly received 

 appears to be true; inasmuch as it is generally believed 

 that when the heart strikes the breast and the pulse is felt 

 without, the heart is dilated in its ventricles and is filled 

 with blood; but the contrary of this is the fact, and the 

 heart, when it contracts (and the impulse of the apex is 

 conveyed through the chest wall), is emptied. Whence the 

 motion which is generally regarded as the diastole of the 

 heart, is in truth its systole. And in like manner the intrin- 

 sic motion of the heart is not the diastole but the systole; 

 neither is it in the diastole that the heart grows firm and 



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