22 MOTION OF THE 



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

 deeper blood-red colour. 



From these particulars it appeared 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 vigour and 

 tenseness, and from soft become hard, prominent and thick- 

 ened: 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 fourth observation 

 preceding, in which we have seen that the heart, by squeezing 

 out the blood 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 re- 

 main 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 pulsation when the heart is tense. 



These things, therefore, happen together or at the same in- 

 stant: the tension of the heart^ the pulse of its apex, which is 

 felt externally by its striking against the chest, the thickening 

 of its parietes, and the forcible expulsion of the blood it con- 

 tains 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 con- 

 tracts [and the shock is given], 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 intrinsic motion of 

 the heart is not the diastole but the systole ; neither is it in 

 the diastole that the heart grows firm and tense, but in the 

 systole, for then only, when tense, is it moved and made 

 vigorous. 



