III. CIRCULATION. 



PA IiT I.— THE MECHANICS OF THE CIRCULATION OF THE 

 BLOOD AND OF THE MOVEMENT OF THE LYMPH. 



A. General Considerations. 



The metaphorical phrase " circulation of the blood" means that every par- 

 ticle of blood, so long as it remains within the vessels, moves along a path 

 which, no matter how tortuous, finally returns into itself ; that, therefore, the 

 particles which pass a given poiut of that path may be the same which have 

 passed it many times already ; and that the blood moves in its path always in 

 a definite direction, and never in the reverse. 



The discoverer of these weighty facts was " William Harvey, physician, 

 of London," as he styled himself. In the lecture notes of the year 1616, 

 mostly in Latin, which contain the earliest record of his discovery, he declares 

 that a " perpetual movement of the blood in a circle is caused by the beat of 

 the heart" ("perpetuum sanguinis motum in circ'ulo fieri pulsu cordis"). 1 

 For a long time afterward the name of the discoverer was coupled with the 

 expression which he himself had introduced, and the true movement of the 

 blood was known as the "Harveian circulation." 2 



Course of the Blood. — The metaphorical circle of the blood-path may 

 be shown by such a diagram as Figure 8. 



If, in the body of a warm-blooded animal, we trace the course of a given 

 particle, beginning at the point where it leaves the right ventricle of the heart, 

 we find that course to be as follows : From the trunk of the pulmonary artery 

 (PA) through a succession of arterial branches derived therefrom into a capil- 

 lary of the lungs (PC) ; out of that, through a succession of pulmonary veins, to 

 one of the main pulmonary veins (PF) and the left auricle of the heart (L A) ; 

 thence to the left ventricle (LV); to the truuk of the aorta (A); through a 

 succession of arterial branches derived therefrom into any capillary (C) not 

 supplied by the pulmonary artery; out of that, through a succession of veins 

 (F) to one of the vena? cava? or to a vein of the heart itself; thence to the 

 right auricle (RA), to the right ventricle (RV), and to the trunk of the pul- 

 monary artery, where the tracing of the circuit began. 



1 William Harvey: Prelectione.s Anatomies, Universal!*, edited, with an autotype reproduction 

 of the original, by a committee of the Royal College of Physicians "f London, 1886, p. 80. 



J Harvey's discovery of the circulation was first published in the modern sense in his work 

 Exercitalio amaiomica de motu cordis ei sanguinis in animalibus, Francofurti, 1628. This great 

 classic <:ui he read in English in the following : On the Motion of the Heart and Blood in Animals. 

 By William Harvey, M. D. ; Willis's translation, revised and edited by Alex. Bowie, 1889. 

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