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timid, arc inspired to perform the most daring actions. But all these 

 passions, all these moral affections, operate only by increasing the action 

 of the heart, by increasing the frequency and the force of its pulsations, 

 so that it excites the brain or the muscular system, by a more abundant 

 supply of blood. 



The heart is not quite ovoid in man as it is in several animals, nor is it 

 parallel to the vertebral column, but it lies obliquely, and is flattened to- 

 wards the side next the diaphragm on which it rests. 



Of the four cavities which form the heart, two are, in a measure, ac- 

 cessary, viz. the auricles; they are small musculo-membranous bags op- 

 posed to each other, receiving the blood of all the veins, and pouring that 

 fluid into the ventricles at the base of which the auricles are, as it were, 

 applied. The ventricles arc two muscular bags separated by a partition 

 of the same nature, and belonging equally to both ; they form the greatest 

 part of the heart, and give origin to the arteries. 



The auricle and ventricle on the right side, are larger than those on 

 the left. But that difference of size depends as much on the manner in 

 which the blood circulates, at the approach of death, as on the original 

 conformation of the lungs. On the point of death, the lungs expand with 

 difficulty, and the blood sent into them, by the contractions of the right 

 ventricle, being no longer able to circulate through them, collects in that 

 cavity, flows back into the right auricle, in which the veins continue to 

 deposit blood, stretches their parietes, and increases considerably the di- 

 mensions of those cavities. The capacity of the right cavities is, how- 

 ever, originally greater than that of the left, and is proportioned to that 

 of the venous system which opens into it. The right cavities of the 

 heart, which might be called its venous cavities, have likewise thinner 

 parietes than the left or arterial, and, in this respect, the same difference 

 is observed, as in the parietes of the arteries and veins. The right ven- 

 tricle having to send the blood destined to the lungs, to a very short dis- 

 tance, and through a tissue easily penetrated, requires but a moderate im- 

 pelling force. 



As, will be shown, in speaking of respiration, a function of which the 

 physiological history is not easily separated from that of the circulation, 

 the heart may further be considered as formed of two parts in contact, 

 the one right or venous, the. other left or arterial. Notwithstanding the 

 juxta position of these two parts of the same organ, they are perfectly 

 distinct,^ and the blood in each cavity is very different from that in the 

 other. The blood, in the adult, can never pass immediately from the 

 one to the other; the right side of the heart receives the blood of the 

 whole body, and transmits it to the lungs; the left side of the heart re- 

 ceives the blood of the lungs, and distributes it over the whole body, so 

 that, in a physiological point of view, the lungs form a part of the circle 

 of the circulation, and serve as an indispensable medium between the 

 two divisions of the heart, and as will be seen hereafter, their part of the 

 circle is, by no means, the least important. 



If there existed, between the ventricles, a direct communication, the 

 venous blood would mix with the arterial, and the union of these two 

 fluids would mutually impair the qualities of each. Recent observations 

 have furnished an opportunity of judging of the effects of such a commu- 

 nication between the ventricles, which had been imagined by the ancients, 

 but of which no case had yet been met with. A man, forty-one years of 

 age, came to the Hopital de la Charite, to undergo the operation of litho- 



