THE HEART'S ACTION. 147 



affinity which is satisfied as soon as the Hood presents itself in the cells 

 of the lungs. Arterialization "being accomplished, the portions to Ibe 

 changed exert a pressure on those that have changed, and the blood, mov- 

 ing forward in the pulmonary veins, reaches the left auricle of the heart. 



For a moment it passes into the left auricle and ventricle continuously, 

 but the auricle, being of less capacity, fills first. It contracts as soon 

 as it is completely full, and drives its contents into the left ventricle, dis- 

 tending it to the utmost. The ventricle now contracts, shutting the mi- 

 tral valve, and the ram-like action is repeated on this side of the heart. 

 But the blood expelled from the ventricle is urged into the aorta, its force 

 being decomposed, as before described, one part acting instantaneously 

 as an impact on the blood, the other on the arterial walls, and on the 

 first moment of the recession of the walls of the ventricle the semilu- 

 nar valves of the aorta shut, and this act completes one tour of the cir- 

 culation of the blood. 



In this description I have said nothing of the circulation in the sub- 

 stance of the heart itself, since it would have led to a needless complica- 

 tion. It should be remembered, as an illustration of the working of the 

 physical principle here explained, that the motion of the blood is contrary 

 in the greater and less circulations, compared together. In the former, 

 the current is from the crimson to the blue, in the latter, from the blue 

 to the crimson side. 



The action of the heart is therefore limited to the filling of the arterial 

 tubes, so as to present to the capillaries a constant supply of Correct state _ 

 blood. There seems to be but little suction force exerted ment of the 

 by the- auricular cavities for the emptying of the veins. The heart ' s action< 

 valvular construction of these vessels economizes every pressure that the 

 muscles may exert on them in favor of the circulation, for every such 

 pressure must, by reason of the valves^ force the blood onward to the 

 heart. This is, however, only an incidental result of the same character 

 a's the influence which the motions of respiration exert. They may be 

 properly overlooked in a general statement of the causes of the circulation. 



By regarding the affinity between the blood and the tissues with which 

 it is in contact as the great primary cause of the circulation, , Various facts 

 we assign a reason for those various phenomena which can supporting this 

 not be accounted for on Harvey's doctrine : the motions in ex P lanatlon - 

 the embryo ; the periodic and local variations ; the portal circulation ; 

 the changes in the current, as seen under the microscope ; the movement 

 in the capillaries after the heart is cut out ; the empty condition of the 

 arteries after death ; the phenomena of acardiac foetuses ; local inflam- 

 mations and congestions ; the gangrene of parts while their capillaries 

 are pervious ; the retardation of the current On the application of cold or 

 cf carbonic acid gas ; the results of asphyxia and death by drowning or 



