174 THE HUMAN HEART. 



the mind just like the lungs, and the spontaneous order of the body 

 would be lost ; in a word, the pulse would coincide with the respi- 

 ration. Even as it is, the respiration exerts a marked influence upon 

 the pericardium, though the heart is not further affected thereby 

 than as it receives the general movements of the lungs and brains, 

 while at the same time it exerts under them its own movements, or 

 maintains its individuality. 



We have now pursued the blood into the trunks of the pulmo- 

 nary veins, where it is still impelled by the vis a tergo, and moreover 

 drawn by the inviting lungs, until it is poured by the four trunks 

 of those veins into the left auricle, which it opens and distends. 

 The auricle now reacts or contracts, and squeezes the blood whither 

 there is the smallest resistance, that is to say, into the left ventricle, 

 which, when filled, in its turn contracts, and its blood shutting back 

 the mitral valves placed between it and its auricle, is driven forwards 

 into the aorta ) again to perform the same revolutions, and to per- 

 petuate life by incessant cycles of formation, destruction and reform- 

 ation. 



From this second view of the circulation we may follow the ac- 

 count given by one physiologist, namely, that the cause of the alter- 

 nate motion of the heart is the action and reaction of the blood and 

 the vessels ; that the immediate cause of the motion of the ven- 

 tricles is the action of the blood and the auricles ; and the immedi- 

 ate cause of the motion of the auricles is the action of the blood 

 and the venae cavae ; further that the immediate cause of the motion 

 of the vena cava is each particular branch of it ; the immediate 

 cause of the motion of the branch is each particular twig of it, and 

 of each capillary tube thereto appended ; the immediate cause of the 

 motion of each venous twig is the action of the little arterial vessel 

 which empties itself into it ; and the immediate cause of this action 

 is the action of the branch, of the trunk, and finally of the heart : 

 wherefore the cause of the heart's motion is continuous, and like the 

 blood itself runs in a circle from the left ventricle, throughout the 

 blood-system, to the right ventricle; showing that there is not a 

 point in the system but contributes to the motion of the heart. We 

 see from this whirl or world of immediate causes how necessarily a 

 motion once begun in these living wheels, rolls onwards, circling 



