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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



in order to discover whether thosehints were val- 

 uable or worthless. Harvey must have learned the 

 views of his master Fabricius ; and it is likely 

 enough that to his acute mind Fabricius's explana- 

 tion of the functions of the valves seemed rather 

 lame. But, as a matter of fact, Harvey did not 

 reason out the circulation from the datum of the 

 valves. On this point his own words, in the pas- 

 sage which contains the fullest account of the 

 considerations which led him to the doctrine of 

 the circulation, leave no doubt whatever : 



"Thus far I have spoken of the passage of the 

 blood from the veins into the arteries, 1 and of 

 the manner in which it is transmitted and distrib- 

 uted by the action of the heart; and thus far 

 some, perhaps, moved by the authority of Galen 

 or of Columbus, or by the reasonings of other au- 

 thors, will agree with me. But when I proceed 

 to what remains to be said concerning the quanti- 

 ty and the origin of the blood thus transmitted 

 (though it is highly worthy of consideration) it 

 will seem so new and unheard of, that I not only 

 fear injury to myself from the envy of a few, but I 

 dread lest I make all mankind my enemies. So 

 much does custom, or teaching once accepted and 

 fixed by deep roots, weigh with all ; and such is 

 the influence of the venerable opinion of antiquity. 

 However this may be, now that the die is cast, 

 my hope lies in the candor of lovers of truth and 

 of learned minds. Indeed, when I thought often 

 and seriously upon how large the quantity [of 

 transmitted blood] is ; upon my dissections of 

 living animals (for the purposes of experiment) 

 and the opening of arteries and the many consid- 

 erations arising therefrom ; as well as upon the 

 magnitude and the symmetry of the ventricles 

 of the heart and of the vessels which enter and 

 leave them (since Nature makes nothing in vain, so 

 great a size proportionally would not be given to 

 these vessels without an ohject) ; and upon the 

 elaborate mechanism of the valves and fibres, and 

 of the rest of the structure of the heart ; as well as 

 of many other things ; and when I long turned over 

 in my mind, what might be the quantity of the 

 transmitted blood, in how short a time its trans- 

 mission might be effected ; whether that quantity 

 could be supplied by the juices of the food in- 

 gested : I came at length to the conclusion that 

 the veins would become collapsed and empty, 

 while the arteries, on the other hand, would he 

 ruptured by the excess of blood poured into them ; 



1 In the preceding chapter (vii.) Harvey has been 

 discussing the passage of the blood through the lungs, 

 supporting his views, among other arguments, by the 

 authority of Galen and of Columbus ; and it must be re- 

 membered that, he termed the pulmonary artery vena 

 arteriosa and the pulmonary vein arteria venosa. 

 Wherefore he properly speaks of the passage of the 

 blood " from the veins into the arteries." 



unless there were some road by which the blood 

 could at length run back from the arteries into 

 the veins, and return to the right ventricle of the 

 heart. So I began to think whether there was a 

 kind of motion as it were in a circle ; this I after- 

 ward found to be true." l 



In all this very full and interesting account 

 of the course of Harvey's inquiry, it will be ob- 

 served that not one word is said about the valves 

 of the veins. The valves of which he speaks are 

 those of the heart, which had been known, as I 

 have pointed out, ever since the days of Erasis- 

 tratus. 



Finally, I venture to affirm that Harvey did 

 not deduce the circulation from the disposition 

 of the valves of the veins, because it is logically 

 impossible that any such conclusion should be 

 deduced from such premises. The only conclu- 

 sion which is warranted by the presence of valves 

 in the veins is, that such valves will tend to 

 place a certain amount of obstacle in the way of 

 a liquid flowing in a direction opposite to that 

 in which the valves are inclined. The amount 

 of obstacle, from mere impediment to absolute 

 barring of the way, will depend upon the form 

 and disposition of the valves ; upon their inertia, 

 or stiffness of motion, in relation to the force of 

 the current of liquid ; and, above all, upon the 

 firmness or yieldingness of the walls of the tube 

 to which they are attached. The valve which 

 hermetically closes the passage through an iron 

 pipe may be of no use in an India-rubber tube. 

 Therefore, unless the action of such valves as 

 exist in the veins were carefully tested by experi- 

 ment on the living animal, any conclusions that 

 might be based upon their presence would be of 

 doubtful value, and might be interpreted either 

 in the sense of Fabricius, or in that of Harvey. 



Moreover, supposing that it could be proved 

 that in those veins in which valves exist the 

 blood can move only in one way, what is to be 

 said about the numerous veins which have no 

 valves ? And, unless we already know upon ex- 

 perimental grounds that the walls of the cavities 

 of the heart contract in a certain definite order; 

 that the arteries are full of blood and not of air ; 

 and a number of other important facts which can 

 only be experimentally determined — what good is 

 it to know that there are valves in the veins ? 

 There are valves in the lymphatics as well as in 

 the veins, and yet any one who concluded there- 

 from that the lymph circulates after the manner 

 of the blood would make a woful mistake. 



1 "Guliclmi Flarveji Exercitationes Anatomies." 

 Exercitatio I., cap. viii., edition 1(J60. 



