CHAPTER II 

 CIRCULATION OF THE BLOOD THROUGH THE HEART 



Discovery of the circulation Physiological anatomy of the heart Tricuspid valve Pul- 

 monic valves Mitral valve Aortic valves Movements of the heart Cardiac cycle 

 Sounds of the heart Frequency of the heart's action Cause of the rhythmical con- 

 tractions of the heart Accelerator nerves Direct inhibition of the heart Work of 

 the heart. 



HARVEY " set forth for the first time his discovery of the circula- 

 tion," in his public lectures in 1616. In 1628, he published the Exer- 

 citatio Anatomica de Motu Cordis et Sanguinis in Aniwalibns. This 

 discovery, from the isolated facts bearing upon it observed by anato- 

 mists to its culmination in the experiments of Harvey, illustrates so 

 well the gradual development of physiological truth, that it does not 

 seem out of place to begin the study of the circulation with a brief 

 sketch of its history. 



The facts bearing on the circulation, developed before the time of 

 Harvey, are chiefly anatomical. The writings of Hippocrates are 

 indefinite on all points connected with the circulatory system ; and no 

 clear and positive statements are to be found in ancient works before 

 the time of Aristotle. The book of Aristotle most frequently quoted 

 by physiologists is his History of Animals ; and in this occurs a passage 

 which seems to indicate that he thought that air passed from the lungs 

 to the heart ; but in his work, De Partibus Animalium, it is stated that 

 there are two great bloodvessels, the vena cava and aorta, arising from 

 the heart, and that the aorta and its branches carry blood. Galen, 

 however, demonstrated experimentally the presence of blood in the 

 arteries, by including a portion of one of these vessels between two 

 ligatures, in a living animal ; but his ideas of the communication be- 

 tween the arteries and veins were erroneous, for he believed in the 

 existence of small orifices in the septum between the ventricles of the 

 heart, a mistake that was corrected by Vesalius about the middle of 

 the sixteenth century. 



In 1546, seven years before the description of the pulmonary circu- 

 lation by Servetus, Rabelais, probably the most learned man of his 

 time, gave a very fair description of the circulation of the blood 

 through the lungs. An account of this, with a literal translation from 



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