32 MOTION OF THE 



powder, it is ignited, upon which the flame extends, enters the 

 barrel, causes the explosion, propels the ball, and the mark is 

 attained all of which incidents, by reason of the celerity with 

 which they happen, seem to take place in the twinkling of an 

 eye. So also in deglutition : by the elevation of the root of the 

 tongue, and the compression of the mouth, the food or drink is 

 pushed into the fauces, the larynx is closed by its own muscles, 

 and the epiglottis, whilst the pharynx, raised and opened by 

 its muscles no otherwise than is a sac that is to be filled, is lifted 

 up, and its mouth dilated ; upon which, the mouthful being re- 

 ceived, it is forced downwards by the transverse muscles, and 

 then carried farther by the longitudinal ones. Yet are all these 

 motions, though executed by different and distinct organs, per- 

 formed harmoniously, and in such order, that they seem to con- 

 stitute but a single motion and act, which we call deglutition. 



Even so does it come to pass with the motions and action of 

 the heart, which constitute a kind of deglutition, a transfusion 

 of the blood from the veins to the arteries. And if any one, 

 bearing these things in mind, will carefully watch the motions 

 of the heart in the body of a living animal, he will perceive not 

 only all the particulars I have mentioned, viz., the heart be- 

 coming erect, and making one continuous motion with its auri- 

 cles; but farther, a certain obscure undulation and lateral incli- 

 nation in the direction of the axis of the right ventricle, [the or- 

 gan] twisting itself slightly in performing its work. And indeed 

 every one may see, when a horse drinks, that the water is drawn 

 in and transmitted to the stomach at each movement of the throat, 

 the motion being accompanied with a sound, and yielding a pulse 

 both to the ear and the touch ; in the same way it is with each 

 motion of the heart, when there is the delivery of a quantity of 

 blood from the veins to the arteries, that a pulse takes place, 

 and can be heard within the chest. 



The motion of the heart, then, is entirely of this description, 

 and the one action of the heart is the transmission of the blood 

 and its distribution, by means of the arteries, to the very extre- 

 mities of the body ; so that the pulse which we feel in the ar- 

 teries is nothing more than the impulse of the blood derived 

 from the heart. 



Whether or not the heart, besides propelling the blood, giving 

 it motion locally, and distributing it to the body, adds anything 



