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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



the works attributed to Aristotle, which consti- 

 tute a sort of encyclopaedia of the knowledge of 

 that tinie, there is evidence that the writer knows 

 as much as has been mentioned, and he refers to 

 the views of his predecessors. Twenty-two hun- 

 dred years ago the sciences of anatomy and phys- 

 iology existed, though they were as yet young, 

 and their steps tottered. 



Aristotle's description of the heart is often 

 cited as an example of his ignorance, but I think 

 unjustly. However this may be, it is certain that, 

 not long after his time, great additions were made 

 to anatomical and physiological science. The 

 Greek anatomists, exploring the structure of the 

 heart, found that it contained two principal cavi- 

 ties, which we now call the ventricles, separated 

 by a longitudinal partition, or septum : the one 

 ventricle is on its left, the other on its right side. 

 It was to the fleshy body which contains the ven- 

 tricles that the ancients restricted the title of 

 " heart." Moreover, there is another respect in 

 which their terminology was so different from 

 that of the moderns that, unless we recollect 

 that the facts may be just as accurately stated in 

 their fashion as in ours, we are liable to fall into 

 the mistake of supposing that they are blunder- 

 ing. 1 What they speak of as the auricles of the 

 heart, we term the appendices of the auricles; 

 and what we call the auricles are, for the ancients, 

 on the right side, a part of the great vein or vena 

 cava, and, on the left side, a part of the arterial 

 system — the root, in fact, of what they termed 

 the arteria venosa. Thus they speak of the au- 

 ricles as mere appendages, or dilatations, situated 

 upon the arterial and venous trunks respectively, 

 close to the heart ; and they always say that the 

 vena cava and the arteria venosa open into the 

 right and left ventricles respectively. And this 

 was the basis of their classification of the ves- 

 sels, for they held all those vessels which, in this 

 sense, open into the right ventricle to be veins, 

 and all those which open into the left ventricle to 

 be arteries. But here a difficulty arose. They 

 observed that the aorta, or stem of the arteries, 

 and all the conspicuous branches which proceed 

 from it to the body in general, are very different 

 from the veins ; that they have much thicker 

 walls, and stand open when they are cut, while 



1 We pay thnt the heart, in man and the hicrher ani- 

 mals, consists of two auricles and two ventricles ; and 

 that each auricle has an appendix in the form of a 

 pouch. We term the vessel which arises from the 

 riaht ventricle the pulmonary artery, because it sup- 

 plies the luncs with blood. Those vessels which bring 

 away the blood from the luEgs to the left auricle we 

 call the pulmonary veins. 



the thin-walled veins collapse. But the " vein " 

 which connected the right ventricle and the lungs 

 had the thick coat of an artery, while the " ar- 

 tery " which connected the left ventricle and the 

 lungs had the thin coat of a vein. Hence they 

 called the former the vena artcriosa, or artery- 

 like vein, and the latter the arteria venosa, or 

 vein-like artery. 



The vena arteriosa is what we call the pul- 

 monary artery, the arteria venosa is our pul- 

 monary vein ; but in trying to understand the old 

 anatomists it is essential to forget our nomen- 

 clature and to adopt theirs. With this precau- 

 tion, and with the facts before our mind's eye, 

 their statements will be found to be, in the main, 

 exceedingly accurate. 



About the year 300 b. c. a great discovery, 

 that of the valves of the heart, was made by 

 Erasistratus. This anatomist found, around the 

 opening by which the vena cava communicates 

 with the right ventricle, three triangular mem- 

 branous folds, disposed in such a manner as to 

 allow any fluid contained in the vein to pass into 

 the ventricle, but not back again. The opening 

 of the vena arteriosa into the right ventricle is 

 quite distinct from that of the vena cava ; and 

 Erasistratus observed that it is provided with 

 three pouch-like, half-moon-shaped valves ; the 

 arrangement of which is such that a fluid can 

 pass out of the ventricle into the vena arteriosa, 

 but not back again. Three similar valves were 

 found at the opening of the aorta into the left 

 ventricle. The arteria venosa had a distinct 

 opening into the same ventricle, and this was 

 provided with triangular membranous valves, like 

 those on the right side, but only two in number. 

 Thus the ventricles had four openings, two for 

 each ; and there were altogether eleven valves, 

 disposed in such a manner as to permit fluids to 

 enter the ventricles from the vena cava and the 

 arteria venosa respectively, and to pass out of 

 the ventricles by the vena arteriosa and the aorta 

 respectively, but not to go the other way. 



It followed from this capital discovery that, 

 if the contents of the heart are fluid, and if they 

 move at all, they can only move in one way; 

 namely, from the vena cava, through the ventricle 

 and toward the lungs, by the vena arteriosa, on the 

 right side ; and, from the lungs, by way of the ar- 

 teria venosa, through the ventricle, and out by the 

 aorta for distribution in the body, on the left side. 



Erasistratus thus, in a manner, laid the foun- 

 dations of the theory of the motion of the blood. 

 But it was not given to him to get any further. 

 What the contents of the heart were, and whether 



