Motion of the Heart and Blood 25 



but the same things are manifest in the heart of small 

 fishes and of those colder animals where the organ is 

 more conical or elongated. 



3. The heart being grasped in the hand, is felt to 

 become harder during its action. Now this hardness 

 proceeds from tension, precisely as when the forearm is 

 grasped, its tendons are perceived to become tense and 

 resilient when the fingers are moved. 



4. It may further be observed in fishes, and the 

 colder blooded animals, such as frogs, serpents, <Scc., 

 that the heart, 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 tense- 

 ness, and from soft become hard, prominent, and 

 thickened : in the same manner the heart. 



We are therefore authorized to conclude that the 

 heart, at the moment of its action, is at once con- 

 stricted 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 remain in doubt of the fact, for if the ventricle 

 be pierced the blood will be seen to be forcibly pro- 

 jected outwards upon each motion or pulsation when, 

 the heart is tense. 



These things, therefore, happen together or at the 

 same instant : the tension of the heart, the pulse of its- 



