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Cornell University Library 
 QP 101.C46 
 
 History of the discovery of the circulat 
 
 3 1924 024 562 187 
 
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 Entered according to Act of Congress, in the year 1884, by 
 
 P. BLAKISTON, SON & CO., 
 
 In the Office of the Librarian of Congress, at Washington, D. C. 
 
HISTORY OF THE DISCOVERT 
 
 CIRCULATION OF THE BLOOD. 
 
The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924024562187 
 
HISTORY OF THE DISCOVERY 
 
 OP THE 
 
 CIRCULATION OF THE BLOOD.* 
 
 In the minds of every one the circulation of the blood is 
 invariably and justly associated with the name of Harvey. The 
 discovery of the circulation, however, like that of all other great 
 discoveries, was not made by Harvey alone. Indeed, the dis- 
 covery of the circulation of the blood, in the widest acceptation 
 of the term, cannot be attributed to any one person, age or 
 country. With the name of Harvey must be associated those 
 of Erasistratus, Galen, Servetus, Ceesalpinus, Malphigi, Aselli, 
 Pecquet, Rudbeck, Bartholinus. The history of the circulation 
 extends, therefore, over a period of 2000 years, from the epoch 
 of the Egyptian Ptolemies to the latter part of the 17th century, 
 and even, in some respects, to the present day. The general 
 structure of the heart ; its cavities ; the play of its valves ; the 
 passage of the blood from its right side to the lungs, and back 
 to its left side, thence through the arteries to all parts of the 
 body; the valves in the veins; the flow of the venous blood 
 toward the heart, had been demonstrated, in an isolated way, by 
 this or that person, before Harvey's time; while it was not until 
 after the appearance of his great work that the discovery of the 
 capillaries made intelligible the manner in which the blood 
 
 * This essay was delivered as a lecture, at the Jefferson Medical College, 
 December 10th, 1883, concluding a course on the circulation, and constitutes, 
 with but little modification, the 25th chapter of a forthcoming work on 
 Physiology, by the author. 
 
 5 
 
CIECULATION OF THE BLOOD. 
 
 passed from the arteries to the veins ; and the demonstration of 
 the lymphatics completed our otherwise imperfect knowledge of 
 the circulation. If, however, the great generalizations as regards 
 the circulation, just referred to, were made either before or after 
 the time of Harvey, naturally, it might be asked what was there 
 left for Harvey to discover? In what does the merit of his 
 great work consist? In that he was the first to describe accurately 
 the motions of the heart, and both the pulmonary and systemic 
 circulations correctly. Without doubt Harvey was the first who 
 described correctly the entire circulation of the blood, under- 
 standing by the word circulation the flowing of the blood from 
 the heart to the lungs, back to the heart, thence through the 
 arteries to the periphery, and from the periphery, through the 
 veins, back to the heart. That is, the flowing of the blood in a 
 circle. It must be remembered, however, that Harvey saw this 
 circulation only in his mind's eye, as the capillaries or connecting 
 links between the arterial and venous systems were not discovered 
 by Malphigi until after Harvey's death. The history of the dis- 
 covery of the circulation of the blood has been often told ; but 
 the subject is one of such interest, extending as it does over a 
 very long period, illustrating so forcibly how slowly truth is 
 attained, that fact after fact must be first established before any 
 generalization can be arrived at; how the isolated, unconnected 
 labors of generations finally culminate, in the hands of a genius, 
 in a grand discovery; that I trust it will not be considered 
 superfluous if I rapidly tell the story of the discovery of the 
 circulation of the blood once more. Although no mention is 
 made of bleeding in the Iliad, that encyclopaedia of the knowl- 
 ,edge possessed by the Greeks in Homer's day, yet there is no 
 .reason to doubt that Podalirius, who attended, as surgeon, the 
 
CIRCULATION OF THE BLOOD. 
 
 hosts of Agamemnon, made use of this practice; as we learn 
 from later sources' that, by bleeding tlie daughter of the King 
 of Caria, he effected a cure, the reward of which was her hand 
 in marriage, and as dowry, the Chersonesus. While the Greeks 
 and the ancients generally were aware that the blood of man and 
 animals coursed in a vast system of tubes, their knowledge of 
 the circulation of the blood extended but a little beyond this. 
 Indeed, their views on this subject were of the most. imperfect or 
 erroneous character. That the blood flowed in certain veins; 
 that there were additional vessels erroneously called arteries, 
 because they were supposed to contain air ; that the heart was a 
 hollow, muscular organ ; constituted about all their knowledge 
 of the circulation.^ This is not to be wondered at, however, 
 since the superstitious respect paid to their dead by the Greeks 
 made dissection an impossibility, the little anatomical knowledge 
 existing in the days of Hippocrates having been derived from 
 
 ' Stephani Byzantini, De Urhibus, Lug Bat. 1694, p. 686. Syrna, urbs Cariae, 
 Condita est autem a Podalirio, Bxpulsum enim in Cariam a caprario euodam 
 servatum, atque ad DamcBthum Cariae regem adductum, cujus filiam Syrnam 
 ex teeto delapsam, ab eo sanatam esse. Sic vero aiunt animum despondente 
 Damcetho, Podallrium ab utroque braohio sanguine ex tracto puellam sani- 
 tari restituisse Damoethum vero admiratum, ei pliam collocasse, ac dedisse 
 Chersonesum. 
 
 Podalirius, exiled in Caria and preserved by a goatherd, was led to 
 DamcBtbus, King of Caria, whose daughter Syrna had fallen from a roof, by 
 him to be cured. Truly, they say that Damoethus was very despondent in his 
 mind, but Podalirius having drawn blood from both arms, restored the girl to 
 health. Damoethus was so much pleased that he gave him the Chersonesus 
 and his daughter in marriage. 
 
 ^ Hippocrates' Opera Omnia, Lug Bat. 1665, p. 275. Envres completes 
 d'Hippocrate, Par B Littrfi, Tomes 8, Paris, 1839-1853. Introduction 
 Tome 1, p. 241. 
 
CIRCULATION OF THE BLOOD. 
 
 the rapid inspection of the viscera of animals sacrificed upon 
 the altar on the occasion of some religious ceremony. Even 
 Aristotle/ whose anatomical knowledge far exceeded that of 
 Hippocrates, advanced but little our knowledge of the vascular 
 system. Aristotle taught that the veins communicate with the 
 heart; that vessels pass from the heart to the lungs, and that the 
 heart and the veins are filled with blood. Such was the limited 
 knowledge of the circulation of the blood as known to the most 
 celebrated of the Greeks. A great advance, however, was soon 
 to be made, not only in anatomy, but in all branches of science. 
 The wonderful campaigns and victories of Alexander, Aristotle's 
 patron, resulting in the conquering of Egypt and the establish- 
 ing of the Macedonian dynasty of kings, and the building of 
 Alexandria, not only revolutionized the political and social world, 
 but influenced all branches of knowledge, in a way and to an 
 extent that modern Europe is only now beginning to appreciate. 
 Under the magnificent patronage of the Ptolemies, the ISIace- 
 donian kings of Egypt, there arose at Alexandria that famous 
 school, the Museum, a centre of learning for the organization and 
 development of all kinds of knowledge, the like of which has 
 never been seen since. Tliere were associated under the hospit- 
 able roof of the Egyptian kings some of the most learned and 
 wonderful men the world has ever seen. The astronomers, Hip- 
 parchus and Ptolemy ; geometers like Euclid and Archimedes ; 
 the engineers and geographers, Apollonius, Erastosthenes ; his- 
 torians like Manetho; the theologian, Cyril ; learned women like 
 Hypatia; the celebrated anatojnists and physicians, Herophilus 
 and Erasistratus. For the practical study of astronomy there 
 were placed beneath the Porch equinoctial and solstitial armils, 
 ^ApiiTTUTs^uui Uspt Zwwv lavopta, Lipsse, 18C9, Lib. in, Cap. ii, in, iv. 
 
CIRCULATIOSr OF THE BLOOD. 
 
 quadrants, dioptras, astrolabes and meridian lines; a botanical 
 garden offered opportunity to those who wished to study plants; 
 a zoological menagerie offered facilities to those interested in the 
 dissection of animals. The library, containing nearly a million 
 volumes, was open (feily to those desirous of making themselves 
 acquainted with the knowledge of the day or of that of antiquity. 
 Vast collections of all kinds of natural objects had been brought 
 there, from every part of the known world, by the Macedonian 
 conquerors, for the use and benefit of the student. At the 
 Museum, in Alexandria, the student found everything that would 
 assist, develop and refine the intellect — the calm, the leisure, the 
 means of living and of study. The usages of that wonderful 
 country, Egypt, where death perpetuates itself in a thousand 
 embalmed forms, had from time immemorial familiarized the 
 vulgar and uneducated with autopsies and dissections. The 
 study of anatomy by the only means possible, the dissection of 
 the dead body, was uo longer regarded with superstitious liorror 
 and considered as sacrilege. Pliny tells us that those intelligent 
 and magnificent princes, the Greek kings "of Egypt, not only 
 lavished their treasure in the interests of science, but personally 
 attended the dissections that were daily conducted at the Museum. 
 The Medical School of Alexandria gave to the world those famous 
 anatomists, Herophilus and Erasistratus.* With them began the 
 
 ^ All that we know of these anatomists is derived from the accounts given 
 of them by later writers, more particularly Galen, Ruffus and Celsus. Among 
 the writings of Galen, especially, there are innumerable allusions to the dis- 
 coveries made in anatomy by Herophilus. Among some of the most import- 
 ant of these may be mentioned the references that are found in Claudii 
 Galeni opera omnia Venetiis, 1556, Tom. 1 and 2 ; De Different Pulsuum, 
 Lib. ini, Cap. 1 and 10; De Anat. Admiuis., Lib. 6, Cap. 8 and 9, and 
 Lib. 9, Cap. 1, 3 and 5 ; and the De Usu Pulsuum, Cap. 4. Reference to 
 
10 CIECULATIOX OF THE BLOOD. 
 
 study of the structure and use of the heart and its great blood 
 vessels, by means of actual dissection. 
 
 The name of Herophilus ought to be familiar to all students 
 of anatomy, as many parts of the human body, such as the 
 Choroid Plexus, the Torcular Herophili, the Calamus Scripto- 
 rius, the Duodenum, etc., were first described by him. The 
 most important contribution that he made to our knowledge of 
 the vascular system was the demonstration of the isochronism of 
 the pulsations of the arteries and of the beating of the heart, and 
 of the latter being the cause of the former, a phenomena that had 
 already been imperfectly referred to by Hippocrates and Aris- 
 totle. Herophilus noticed also the difference in the thickness of 
 the walls of the arteries and of the veins, and described the 
 vessels connecting the heart and the lungs, distinguishing the pul- 
 monary artery from the pulmonary vein, designating the former 
 as the arterial vein and the latter as the venous artery. 
 
 To Erasistratus, one of the most distinguished of the anato- 
 mists of the Alexandrian school, and one of the most celebrated 
 physicians of antiquity, science is indebted for the discovery of 
 
 the same discoveries and views of Herophilus is made by Ru£Fus. MedicsB 
 artis principes, 1567, Henricus Stephanus. Ru£6i Ephesii Medici de appel- 
 lationibus partium, Lib. 1, Cap. xvi, xxii, Lib. ii, Cap. ill, xvii. Celsus 
 refers to the vrell known but not usually credited story of Herophilus and 
 Erasistratus having dissected human criminals, in the enthusiasm engendered 
 by their study of the human body. The passage will be found in Aurelii 
 Cornelii Celsi de re medioa libri octo, Prajfatio in Med. art. princip. While 
 both RufFus and Celsus refer to Erasistratus, almost all our knowledge of 
 his discoveries is based upon what is contained in Galen. Among the many 
 passages in the different works of Galen referring to Erasistratus, I will only 
 mention the following: Au Sanguis Natura, Cap. 2; De different puis.. 
 Book iiii. Cap. 10 i De utilitate respirat,, Cap. 1 ; De Hipp et Plato decret., 
 Lib. VI, Cap. 6, — Galenus edit, cit. 
 
CIECCLATION OP THE BLOOD. 11 
 
 the valves of the heart, and their function iu the circulation. 
 "We have stated in a previous lecture that there is reason to 
 believe that Erasistratus had seen the lacteals a dependence, so 
 to speak, of the vascular system, even though he had misunder- 
 stood their use, and we shall see hereafter that he appears also 
 to have distinguished the sensory from the motor nerves. While 
 there is no doubt that the anatomists and physiologists of anti- 
 quity distinguished two kinds of vessels, arteries and veins, their 
 very name, artery, from the Greek arjp, air, and rripew, I carry, 
 conclusively proves how absolutely ignorant they were of the 
 true functions of these vessels. Hippocrates, Aristotle, and more 
 especially Erasistratus, believed that the arteries, as their name 
 implies, carried air. This error was due, no doubt, to the fact 
 that when a dead body is opened the arteries are usually found 
 empty ; and to the theory that the air in these vessels came, 
 originally, from the trachea, hence the name of tracheal artery, 
 by which it is designated by the French, even at the present day. 
 Erasistratus' supposed the air passed from the trachea into the 
 pulmonary veins (his venous artery), from there to the left side of 
 the heart, and thence, by the arteries, to all parts of the body. 
 Substitute for the air oxygen, and for his venous artery pulmo- 
 nary capillaries, and the much-abused theory of Erasistratus 
 becomes the modern one of respiration. Although during the 
 four centuries that followed the brilliant epoch of the Alexan- 
 
 ^Galenus edit. dt. De utilitate respirationis, Cap. 1. " Queenam est 
 utilitas respirationis .... Nam animae ipsius generatio est ... . An 
 innati caloris ventilatio ac refrigeratio .... Aut horum quidem nihil est 
 varum arteriarum expletionis gratia respiramus velut Erasistratus putat." 
 
 Galenus edit- dt. An Sanguis in arteriis, Cap. 2. " Enim sicuti Erasis- 
 tratus putat ex ambieute nos sere intra corpus assumpto primo in pulmonem 
 deinde in cor ortas que ab eo arterias." 
 
12 CIRCULATION OF THE BLOOD. 
 
 drian school just described, dissection had gradually fallen into 
 disuse, nevertheless the most famous anatomist of antiquity, 
 Gralen, learned his anatomy in Egypt, where he devoted many 
 years to anatomical studies. His dissections, however, appear to 
 have been limited to animals. By ligating in a living animal, 
 an artery in two places, and opening the vessel between the 
 ligatures, Galen* demonstrated that the vessel contained blood. 
 Thus, by an experiment upon a living animal, a vivisection, the 
 first great source of error, that of supposing that the arteries 
 contained air, was removed, the true nature of an artery demon- 
 strated, and the modern theory of the circulation of the blood 
 made possible. Too much importance cannot be attached to this 
 cardinal experiment of Gfilen. It is evident that as long as it 
 was believed that the veins alone carried blood, and that the 
 arteries only contained air, the discovery of the circulation was 
 an impossibility. 
 
 For 1300 years, in anatomical and physiological matters, the 
 authority of Galen was supreme. With the truths discovered by 
 this most deservedly famous physician, were perpetuated errors, 
 among which was Galen's theory that the air inspired did not 
 enter the body to any extent, as Erasistratus supposed, but was 
 at once rejected after having performed its office, which was that 
 of cooling the body, and that the cavity of the right ventricle 
 of the heart communicated with that of the left ventricle by 
 
 ' Gahnus edit. cit. an sanguis in arteriis nahtra contineatnr Cap. 6. 
 
 "Nam ubi funiculo dissectam arteriam utrinque ligavjmus et quod in 
 medio comprehensum fuerat incidimus sanguine plenam ipsam esse monstra- 
 vimus." 
 
 'Oalenus edit. cit. an sanguis dec, Cap. 6. 
 
 " Qui cor inquiunt non seris substantiam exposcere sed frigidetatem solum 
 modo qua recreare desiderat atque hunc esse respirationis usum." 
 
CIRCULATION OF THE BLOOD. 13 
 
 means of holes in the septum.^ It is true that no one had ever 
 seea these holes in the septum, separating the ventricle; even 
 Galen himself did not claim that he actually saw them; but the 
 theory in Galen's time, and many a day afterwards, was, that 
 the spirituous blood of the left ventricle^ must be mixed with 
 the coarser blood of the right ventricle, that the latter should 
 fulfill its function in nutrition.' Now the only way that theory 
 could account for this mixing of these two kinds of blood was on 
 the supposition that the septum of the ventricle was perforated 
 with holes, through which part of the blood passed from one 
 ventricle to the other, the rest of the blood passing through the 
 pulmonary artery to the lungs. 
 
 Men saw, or believed they saw, what theory demanded they 
 ought to see. As has been too often the case, as the history of 
 science teaches us, the theory did not follow from the facts, but 
 the facts were made to suit the theory. Further, when it is 
 remembered that for sixteen centuries, during the period extend- 
 ing from the epoch of the Alexandrian Museum to that of the 
 School of Salerno, in 1224,'' or more probably to that of Mun- 
 dini, in 1306,^ the human body had never been dissected, it is 
 not to be wondered at that the grossest ignorance of anatomy 
 
 ^Galenus Edit. cit. Ve usu partium, Lib, 6, Cap. 17. " Quse igitur in 
 corde apparet foramina ad ipsius potissimum medium septjim prsedictse 
 coramunitatis gratia extiterunt." 
 
 'Be usu part., Lib. 6, Cap. 17. "Spiritus animalis exhalatio qusedam est 
 sanguinis benigni." 
 
 ^De usu part., Lib. 6, Cap. 16. "Atquse arterise quidem tenuem ac 
 purum et vaporosum participat sanguinem vens autem paueum, eundam 
 que caglinosum serem." 
 
 * Heeser, Geschichte der Medeein, Jena, 1875, pp. 733-738. Corradi, Een- 
 diconde del R. Institut. Lombardo, Ser. ii, Vol. vi. 
 
 ^ Hyrtl, Das Arabische und Hebraische in der Anatomie, Wien, 1879, p. xi. 
 
14 CIRCULATION OF THE BLOOD. 
 
 should have universally prevailed. The horror with which dis- 
 section was regarded, and the limited number of subjects obtain- 
 able for study, will be appreciated from the fact that Mundini, 
 who was Professor of Anatomy at Bologna during the latter part 
 of the 13th and beginning of the 14th century, had dissected in 
 eleven years only three human bodies. Berenger de Carpi, who 
 also occupied the Chair of Anatomy in Bologna a century later, 
 had better opportunities of study than Mundini, whose works he 
 commentated, he having dissected a hundred bodies; and yet 
 the authority of Galen had such weight with de Carpi, that he 
 states that there are certainly holes in the septum separating the 
 ventricles. He adds, however, as if he had an uneasy suspicion 
 as to the truth of the statement, that these holes are seen in man 
 with great difficulty.* 
 
 A short time, however, after the publication of De Carpi's 
 work, viz., in 1553, there appeared the Christianismi Restitutio 
 of the Spaniard, Michael Servetus, whose career reads rather 
 like that of the hero in some romance than of a real historical 
 personage. Educated for the priesthood at Saragossa, relinquish- 
 ing such studies for that of the law, at Toulouse; accompanying, 
 as secretary, Quintana, Confessor to Charles V, upon the occasion 
 of the imperial coronation at Bologna; and going afterwards to 
 the Diet of Augsburg; giving up the prospect of a diplomatic 
 career for that of a theologian; leaving Switzerland and chang- 
 ing his name to Villanovus, to avoid persecution; supporting 
 himself as a proof-reader and editor of learned books while a 
 
 ^Berenger de Carpi. Commentarii cum amplissismua adJitionibus super 
 auatomia Mundini. Bologna 1521 p. cccxli. 
 
 Ista substantia dividit ventrem dextrem a sinistro et in ista substantia sunt 
 certe porositates — sed in homine cum maxima difficultate videnter. 
 
CIECULATION OF THE BLOOD. 15 
 
 student of medicine in Paris; receiving his degree of doctor in 
 medicine; writing works on medical subjects, and practicing 
 medicine with great success for a number of years; returning to 
 the study of theology again, his career of usefulness is suddenly 
 cut short by death at the stake; Servetus, as is well known, 
 being burned alive, in 1553, at Geneva, for heresy, as the author 
 of the Christianismi Restitutio. This work, as its name implies, 
 is a theological treatise, but is also of the greatest interest to the 
 physiologist, as in discussing the nature of the vital spirit, and 
 the manner in which it is elaborated, Servetus describes the 
 flow of the blood from the right ventricle of the heart, l)y the 
 pulmonary artery, through the lungs, and by the pulmonary 
 veins to the left ventricle; distinctly stating that the blood 
 does not pass from the right ventricle to the left through the 
 septum of the heart, as is commonly believed, but by a long 
 passage through the lungs, from the right ventricle, and that it 
 is in the lungs that the blood is agitated, prepared and changes 
 its color, thence passing to the left ventricle by the pulmonary 
 veins. Servetus was not only the first to describe, therefore, the 
 flow of the blood from the right side of the heart, through the 
 lungs, to the left, and the imperviousness of the septum of the 
 heart, but was also the first to point out the place where the 
 venous was changed into arterial blood, the significance of which 
 discovery was neither understood nor appreciated for more than 
 a century afterwards. Further, Servetus adds that the left ven- 
 tricle is not sufficiently capacious for so copious a mixture, nor 
 will it suifice for the elaboration of the color; and that the 
 septum is neither fit for the communication nor the elaboration 
 of the blood, even if any may exude through it. Servetus 
 evidently does not consider that any blood passes through the 
 
16 CIRCULATION OF THE BLOOD. 
 
 septum of the heart, for he most distinctly says that none does 
 so, and in confirmation of his view adds that even if any blood 
 did pass through the septum, the left ventricle is not adapted to 
 its elaboration. That Servetus did not hold the view of Galen, 
 of part of the blood passing through the pulmonary artery and 
 part through the septum, is evident from what Servetus says, 
 that if any one compares his views with Galen's (and no one 
 understood Galen better than Servetus), he will perceive clearly 
 the truth not observed by Galen himself. As comparatively 
 few persons have the opportunity of examining an original copj 
 of the Christianismi Restitutio of Servetus, and as the passag< 
 in that work to whicli I have referred is often imperfectly or 
 incorrectly quoted, I will give it exactly, as I copied it from the 
 original copy in the National Library, at Paris. For this privi- 
 lege I am indebted to Mr. George A. Barringer, one of the 
 librarians of that noble institution, who also afforded me the 
 opportunity of comparing the Nuremberg reprint, of 1791, of 
 the Restitutio, with the original copy of 1553; as well as of 
 consulting many rare and interesting works on the circulation. 
 The celebrated passage upon the pulmonary circulation, in the 
 Restitutio, is found in Liber Quintus, De Trinitate Divina, In 
 quo agitur de Spiritus Sancto, p. 170, and is as follows: — 
 
 "Ad quem rem est prius intelligenda substantialis generatio 
 ipsius vitalis spiritus^ qui ex sere inspirato et subtiilissimo san- 
 guine componitur et nutritur, Vitalis spiritus in sinistro cordis 
 ventriculo suam originera habet, juvantibus maxime pulmonibus 
 ad ipsius generationem. Est spiritus tenuis, caloris vi elaboratus, 
 flavo colore, ignea potentia, ut sit quasi ex puriori sanguine 
 lucidus vapor, substantiam in se continens aquse, seris et ignis. 
 Generatur ex facta in pulmonibus mixtioue inspirati seris cum 
 
CIECTJLATION OF THE BLOOD. 17 
 
 elaborate subtili sanguine, qiiem dexter ventriculus cordis sinistro 
 communicat. Fit autem communicatio hfee, non per parietem 
 cordis medium, ut vulgo c'reditur. Sed magno artificio a dextro 
 cordis ventriculo, longo per pulmones duetu, agitatur sanguis 
 subtilis; a pulmonibus prseparatur, flavis efficitur, et a vena 
 arteriosa in arteriam venosam transfunditur. Deinde in ipsa 
 arteria venosa inspiratio seri miscetur, expiratione a fulgine 
 repurgatur. Atque ita tandem a sinistro cordis ventriculo totum 
 mixtum per diastolem attrahitur apta supellex, ut fiat spiritus 
 vitalis. Quod ita per pulmones fiat communicatio et praeparatio, 
 docet conjunctio varia et communicatio vense arteriosae cum arteria 
 venosa in pulmonibus. Confirmat hoc magnitude insignis vense 
 afteriosae, qua nee talis, nee tanta facta esset, nee tantam a corde 
 ipso vim purissimi sanguinis in pulmones emitteret, ob solum 
 eorum nutrimentum, nee cor pulmonibus hoc ratione serviret; 
 cum prasertim antea in embryone solerent pulmones ipsi aliunde 
 nutriri, ob membranulas illas, sen valvulas cordis usque ad 
 horam nativitalis nondum opertas, ut docet Galenus, Ergo ad 
 alium usum effunditur sanguis a corde in pulmones hora ipsa 
 nativitatis, et tam copiosus. Item a pulmonibus ad cor non 
 simplex aer, sed mixtus sanguine mittitur per arteriam venosam, 
 ergo in pulmonibus fit mixtio. Fiavus ille color a pulmonibus 
 datur sanguine spirituoso, non a corde. In sinistro cordis ventri- 
 culo non est locus capax tantse et tam copiosse mixtionis, nee ad 
 flavum elaboratio ilia sufficiens, Demum, paries ille medius, cum 
 sit vasorum et facultatem expers, non est aptus ad communica- 
 tionem et elaborationem illam, licet aliquid resudare possit. 
 Eodem artificio, quo in hepate fit transfusio a vena porta ad 
 venam cavam propter sanguinem, fit etiam in pulmone transfusio 
 a vena arteriosa ad arteriam venosam propter spiritum. Si quis 
 
18 CIECULATIOIT OF THE BLOOD. 
 
 hsec conferat cum iis quae scribit Galenus lib. vi, et vii, de usu 
 partium, veritatem penitus intelliget, ab ipso Galeno non anim- 
 adversam. Ille itaque spiritus vitalis a sinistro cordis ventriculo 
 in arterias tolius corporis deinde transfunditur." Which may be 
 literally, if not elegantly, translated as follows: — 
 
 "For which purpose the substantial generation of the vital 
 spirit itself is first to be understood, which is composed of and 
 nourished by the inspired air and most subtile blood. The vital 
 spirit has its origin in the left ventricle of the heart, the lungs 
 aiding, to the highest degree, in its generation. The spirit is 
 subtile, elaborated by the force of heat, of a yellowish color, 
 with the power of fire, to the end that it may be, as it were, a 
 bright vapor from the purer blood, containing in itself the sub- 
 stance of water, air, and of fire. It is generated, in fact, in the 
 lungs, with the mixture of inspired air with the elaborated, 
 subtile blood, which the right ventricle of the heart communi- 
 cates to the left. Yet this communication is made, not by the 
 middle wall of the heart, as is commonly believed, but the subtile 
 blood is driven, by a great plan or device, from the right ven- 
 tricle of the heart, by the long passage through the lungs; is 
 prepared in the lungs; the yellow color is made, and it is poured 
 out from the arterial vein (vena arteriosa or pulmonary artery) 
 into the venous artery (arteria venosa or pulmonary vein); there 
 is mixed in the venous artery itself with the inspired air; is 
 purged by expiration of its fuliginous matter ; and so, at length, 
 the whole mixture is attracted by the diastole from the left 
 ventricle of the heart, a fit stufiF out of which to make vital spirit. 
 The various connection and communication of the arterial vein 
 with the venous artery teaches that the communication and 
 preparation is made by the lungs in this manner. The remark- 
 
CIRCULATION OP THE BLOOD. 19 
 
 able size of the pulmonary artery confirms this, which would 
 be neither made in such a way nor so large, nor would there be 
 emitted so great a mass of blood from the heart itself into the 
 lungs, if for the nourishment of these alone, nor would the 
 heart serve the lungs in this manner, since especially before, in 
 embryo, the lungs themselves are accustomed to be nourished 
 from elsewhere, on account of those little membranes, or valves 
 of the heart, not yet being open until the hour of birth, as Galen 
 teaches. Therefore the blood is poured forth, and so copiously, 
 from the heart into the lungs at the hour of birth, for another 
 use. The air also is sent from the lungs to the heart by the 
 venous artery, not pure, but mixed with blood; therefore the 
 mixture is made in the lungs. That yellow color is given to the 
 blood by the lungs, not by the heart. The space in the left 
 ventricle is not capable of holding so great and so capacious a 
 mixture, nor is sufficient for that elaboration of color. Finally, 
 that middle wall, as it is wanting in vessels and power, is not fit 
 for that communication and elaboration, even if some might 
 sweat through. By the same plan by which the transfusion is 
 made from the vena porta to the vena cava, with reference to the 
 blood, so the transfusion from the arterial vein to the venous 
 artery is made in the lungs, with reference to the spirit. If any 
 one compares this with that which Galen writes, Lib. vi, et vii, 
 on the use of the parts, he easily perceives the truth, not observed 
 by Galen himself. And so the vital spirit from the left ventricle 
 of the heart is thence poured out into the arteries of the whole 
 body." 1 
 
 ' I take this opportunity of acknowledging my indebtedness to Mr. John 
 SwalJy, who on this occasion, as well as on numerous others, has given me 
 the benefit of his critical knowledge of the Greek and Latin languages. 
 
20 CIECULATION OF THE BLOOD. 
 
 The Christianismi' Eestitutio is a very rare work. At the 
 present moment there are, indeed, only three original copies 
 known to exist — one in the National Library at Paris, one in 
 the Imperial Library at Vienna, and one in the Library of the 
 University of Edinburgh. The copy in Paris probably belonged 
 to Colladon, Calvin's lawyer, since his name is in it, and was in 
 the possession of the celebrated Dr. Mead, of London, in the 
 early part of the eighteenth century, from whose hands it passed 
 successively through those of De Boze, De Cotte, Gaignat, 
 la Vaillere, finally becoming the property of the National 
 Library. There is not the- slightest reason to suppose that 
 the Paris copy of the Restitutio was ever in the flames that 
 enveloped its author, as is picturesquely described by Flourens,^ 
 the blackness on the pages being due, not to fire, but possibly 
 to dampness.' 
 
 It is usually supposed that the Paris copy of the Restitutio, 
 once in the possession of Dr. ]\Iead is the identical one that 
 disappeared from the library of the Landgrave of Hesse Oassel. 
 However that may be, there can be no doubt that there was a 
 copy of the Restitutio in the Library at Hesse, in the 17th 
 century, as it was from this copy that Wotton obtained the 
 quotation (though he never saw the original) that is to be found 
 on the margin of page 230 of his " Reflections upon Ancient 
 and Modern Learning, the second edition, with large additions, 
 London, 1697." In referring to this quotation, p. 230, Wotton 
 simply observes tiiat he got it from Mr. Charles Bernard, who 
 "had it from a learned friend of his, who had himself copied it 
 from Servetus." In the postscript of the "Reflections" Wotton, 
 
 "■ Histoirfe de la deconverte de la Circulation du Sang, Paris, 1857, p. 155. 
 ^ Henri ToUin, Die Entdeckung des Blutkreislaufs, durch Michael Servet. 
 Jena, 1876, p. 69. 
 
CIRCULATION OF THE BLOOD. 21 
 
 however, at page xxv, states that the quotation from Servetus 
 "was 'copied long ago, by that worthy member of the Royal 
 Society, Mr. Abraham Hill, from whom Mr. Bernard had it. 
 My Lord Bishop of Norwich, whose incomparable library con- 
 tains everything that is rare and excellent, did me the honor to 
 show it me. His manuscript copy is a transcript of that printed 
 one which is preserved in the Landgrave of Hesse's library, at 
 Cassel, the very book that was perused by Saridius, who gives 
 an account of it in his Bibliotheca Anti-Trinitariorum." It is 
 very evident, therefore, that Wotton was not the first, as is often 
 said, to make known to the republic of letters the existence of a 
 copy of the Christianismi Restitutio of Servetus, since he states 
 that Sandius gives an account of it. The reference of Sandius 
 to the Christianismi Restitutio mentioned by "Wotton, is to be 
 found on p. 14 of the Bibliotheca Anti-Trinitariorum Opus 
 Posthumum Christophori Chr. Sandii Freistadii, 1684, and is as 
 follows: "Asservatur unum ejus exemplar in Bibliotheca Illus- 
 trissimi Principis Hassise qase est Casselis." Sandius, in this 
 article, gives a short account of the life, as well as of the works, 
 of Servetus. I may mention here, incidentally, that the quota- 
 tion from Servetus, as given by Wotton, differs a little from the 
 text of the Paris copy. This may be due to carelessness on 
 the part of whoever made the transcript. Curiously enough, the 
 Vienna copy of the Restitutio was once in London, as well as 
 the Paris one; Markos Ivanayi, a Transylvania gentleman, 
 residing in London in 1665, possessing it. He afterwards gave 
 it to the congregation at Claudiopolis, who presented it, through 
 their Superior, to Count Teleki de Izek, who presented it. in 
 turn, to Joseph Second, Emperor of Austria. It was in this 
 way that the library in Vienna cat^e to have a copy. It was 
 
22 CIRCULATION OF THE BLOOD. 
 
 from this copy that the Nuremberg reprint of 1791 was made. 
 The third copy, that in the Edinburgh University library, is 
 imperfect, unfortunately wanting the title-page and first sixteen 
 pages. Otherwise the copy is in good condition. Of its history 
 nothing is known, except that it was presented by Dr. George 
 Douglas, in 1695. 
 
 It is usually stated that of the thousand copies of the Chris- 
 tianismi Restitutio that were known to have been printed, four 
 or five only escaped destruction, including the three that are 
 now known to exist, and as these three copies for a long time 
 remained unknown, the inference is drawn that the Christian- 
 ismi Restitutio did not influence, in any way, the progress of 
 Physiology. It must not be forgotten, however, that in the 
 distribution of the Restitutio, two hundred copies were sent to 
 Frankfort, the headquarters of the book trade, and that it was 
 not until several months afterwards that the existence of these 
 copies became known to Calvin, who requested to have them 
 destroyed. To express, in Geneva, a wish to have two hundred 
 copies of a book destroyed in Frankfort, months after the books 
 had arrived there, is a different matter from the actual destruc- 
 tion of the books, and it has always been a matter of doubt 
 with me as to whether all of those two hundred Frankfort copies 
 were destroyed. Indeed, it would be worth while ransacking the 
 European libraries with a view of learning if there are still 
 existing any undescribed copies of the Restitutio. As a matter 
 of fact, it was in this way that the public learned of the exist- 
 ence of the Edinburgh copy. Prof. Turner requesting Mr. Small, 
 the .librarian, to look if there was a copy in the library of the 
 University of Edinburgh.^ It is quite natural to suppose that 
 ' AthenEeum, London, 1878. 
 
CIRCULATION OF THE BLOOD. 23 
 
 both the enemies and friends of Servetus should wish to obtain 
 a copy of the Restitutio, for the writing of which the author 
 was being tried for his life at Geneva. All Switzerland was 
 alive with excitement in reference to Servetus, both on theo- 
 logical and political grounds. The interest in his views and his 
 fate extended to both Germany and Italy. Just in proportion, 
 therefore, as efforts were made to suppress the work, so would 
 the desire to obtain it be increased, and I can hardly suppose 
 that, under the circumstances, the Frankfort bookseller would 
 not have disposed of some copies, particularly if it could have 
 been managed quietly and with great profit, especially before the 
 intimation had been received that it would be safer to destroy 
 the books rather than sell them. Even if a copy of the Resti- 
 tutio was not obtainable in France, Switzerland, Germany, or 
 Italy, it cannot be doubted but that the views of Servetus were 
 well known to the learned men of those countries, since Servetus 
 had sent manuscript copies of his work, not only to Calvin, in 
 Geneva, but also to Melancthon, in Germany, and even to 
 Curio' in Padua, Italy; and it is not likely, either, that his old 
 friends, who permitted him to escape from France, would not 
 have retained some memento of their physician. It is hardly to 
 be supposed that the possessors of these manuscripts or copies 
 of the Restitutio itself never showed them to any one. So far 
 from the views of Servetus not being generally known to the 
 learned men of the day, the state of public opinion, as expressed 
 shortly after the death of Servetus, seems to me to prove that 
 exactly the opposite was the case, and that of all places, Padua 
 would be the one where new views upon the circulation of the 
 
 ^ ToUin, Colombo Matteo Realdo, in Pfluger's Archiv, Band 27, 1880, 
 pp. 278 and 279. 
 
24 CIECULATION OF THE BLOOD. 
 
 blood would attract the greatest attention. To say the least, it 
 is certainly a curious coincidence that the great advance in our 
 knowledge of the structure of the heart and the passage of the 
 blood through it, should have been made by Vesalius, Colombo, 
 Csesalpinus, etc., within a few years after the printing of the 
 Christianismi Restitutio of Servetus. 
 
 In the year 1555, two years after the printing of the Chris- 
 tianismi Restitutio, there appeared the second edition of the mag- 
 nificent Anatomy of Vesalius, which differed in many important 
 respects from the first edition of 1543; among others, as regards 
 the description of the heart. In the 1555 edition, Vesalius 
 begins by saying that, influenced by the views of Galen, he con- 
 sidered that the blood passed from the right to the left ventricle 
 of the heart, through the septum, by means of the pores. He 
 io^mediately adds, however, that the septum of the heart is as 
 thick, dense and compact as the rest of the heart, and that 
 not the smallest quantity of blood passes through the septum. 
 There can be no doubt that Vesalius held that the septum of the 
 heart was imperforate, in this (the 1555) edition, but the passage 
 in which he maintains this view is not to be found in the 1543 
 edition; and yet, in all of the accounts of the history of the 
 circulation with which I am familiar, that of Tollin' excepted, 
 the views of Vesalius in reference to the imperviousness of the 
 septum of the heart (printed in 1555),^ are said to have preceded 
 
 ^ Die Entdeckung des Blutkreislaufs, Jena, 1876, p. 26. 
 
 '^AndrecE Vesalii, De Humani corporis fahrica Libri septem, Basilece, 1555. 
 " Qui aptius impetu post modum per arterias ferri possit reddens. Maxima 
 portione per ventriculorum cordis septi poros in sinistrum ventriculum desu- 
 dare sinit, p. 743. 
 
 In cordis itaque constructionls ratione, Ipsius que partlum usu recensendla, 
 magna ex parte. Galeni dogmatlbus sermonem accommodavl. * * * * 
 
CIECULATION OF THE BLOOD. 25 
 
 those of Servetus (printed in 1553). The only way in which I 
 can account for this error is by supposing that the historians of 
 the circulation, in quoting Vesalius, have made use of the 1555 
 or 1725 editions, and not that of 1543. Certainly Servetus did 
 not learn his anatomy from Vesalius, since they were at the same 
 time prosectors for Guntherus, Professor of Anatomy in the 
 Medical School of Paris; and as to Servetus' knowledge of prac- 
 tical anatomy, there can be no doubt, Guntherus testifying to 
 that.* On the other hand, Vesalius was probably entirely 
 ignorant of what his former associate in the dissecting-room had 
 published about the heart. Thus Ceradini (Difesa della mia 
 Memoria Geneva, 1870, pp. 126-130), while admitting that 
 it is in the 1555 edition of his Anatomy that Vesalius describes 
 the imperviousness of the septum of the heart, nevertheless 
 claims that Vesalius had discovered this in 1546. Ceradini 
 supports his view by reference to the letter "De chynse radice," 
 
 * * * Haud enim leviter studiosis expendendum est ventriculorum cord s 
 interstitium aut septum ipsum que sinistri ventriculi dextrum latus quod aequo 
 crassum compactum que ac densum est, atque roliqua cordis pars sinistrum 
 ventriculum complectens adeo ut iguorem (quicquid etiam de foveis hac in 
 sede commenter & vena portae ex ventriculo & intestinis suctionis non sim 
 immemor) qui per septi illius substantiam ex dextro ventriculo in sinistrum 
 vel minimum quid sanguinis assumi possit praecipui quum tam patentibus 
 orificis vasa cordis in suorum ventriculorum amplitudinem dehiscant ut mode 
 taceam verum venae cavae ex corde progressem, p. 746. 
 
 '^ Haller Biblioiheca Anatomica, Tomus I, Tiguri, 1774. Verum &c. ipse 
 in praefatione fateter, se Vesalio et Serveto in administrationibus usum esse, 
 eorum que ope partes corporis humani a se ostensas &c. vas a spermatica 
 inventa iterum Vesalio tribuit, p. 174. 
 
 In villa nova Arragoniae civitate natus passim patriae, nomen gessit, aeris 
 ingeuii vir et anatomes minime imperitus quern J. Guintherus secundo a 
 Vesalio loco inter eos discipulos numerat qui sibi adsgumento ftierunt, p. 204. 
 
26 OIECULATION OF THE BLOOD. 
 
 written by Vesalius, ia 1546 to Roelants, and to the Apologia 
 Francisci Putei pro Galeno in anatome exanaen, Venetiis, 1564, 
 written by Vesalius, under the name of Gabriele Cuneo, one of 
 his disciples. Both of these works are to be found in Vesalius' 
 Opera Omnia, Lug Bat. 1725, Tomus Seeundus, pp, 569, 864. 
 Admitting, as Ceradini thinks, that these two works, taken 
 together, prove that Vesalius had demonstrated to his colleagues 
 the imperviousness of the septum upon the cadaver, at Pisa, in 
 1546 (before he left Italy to establish himself at the court of 
 Charles V), it follows that Vesalius was not indebted to Servetus 
 for the demonstration, but, inasmuch as his description was not 
 printed till 1555, the priority of the discovery must be accorded 
 to Servetus in 1553. 
 
 While to my mind there is no doubt that the pulmonary circu- 
 lation was Correctly described by Servetus, beyond statements 
 like that of the blood being transmitted by the left ventricle to 
 the aorta, and thence through the arteries to the whole system, 
 and of the blood flowing from the vena porta through the liver 
 to the hepatic vein, etc., I can find nothing in his work to warrant 
 the idea that Servetus had any idea of the so-called systemic or 
 general circulation. Further, it is not to be supposed that Ser- 
 vetus understood the exact manner in which the blood passed 
 from the pulmonary arteries to the veins, since the capillaries 
 were not discovered by Malphigi for more than a century after- 
 wards. 
 
 Six years after the death of Servetus, that is, in 1559, the 
 pulmonary circulation was re-described by Colombo, who tauf^ht 
 anatomy at Padua, Pisa and Rome. In a work on anatomical 
 subjects, Colombo, in speaking of the heart, observes that between 
 the ventricles a septum is present, through which almost every 
 
CIRCULATION OF THE BLOOD. 27 
 
 one believes that the blood passes from the right ventricle of 
 the heart to the left, but that really the blood goes through the 
 pulmonary artery to the lungs, and is then carried, with the air, 
 by the pulmonary vein, to the left ventricle of the lieart, and that 
 no one had previously observed or described this.' Colombo, 
 however, is evidently wrong when he says no one had previously 
 observed or described this. It is possible that Colombo was 
 ignorant of what Servetus had written in his Christianismi 
 Restitutio, but it certainly appears to me very extraordinary, if 
 such was the case, for Colombo was the pupil of Vesalius, and 
 taught, as prosector and professor, for years, in Padua, the very 
 city where we have seen Servetus had sent one of the manuscript 
 copies of his work, and where his views were well known. To 
 suppose that Colombo was ignorant of the discovery of the 
 pulmonary circulation by Servetus, seems to me to be almost 
 incredible. There was one very good reason, however,^ for 
 Colombo not mentioning Servetus, if he was acquainted with his 
 views; and that was the fear of being burned. Colombo ran no 
 risk in describing the pulmonary circulation, bu.t had he given 
 Servetus as his authority he would have at once been accused 
 of heresy, on the ground that if he regarded Servetus as an 
 
 ^Realdi Columhi Cremonensis in alino Oymnaso Romano Anatomici cele- 
 berimmi De Be Anatomica, Libn xe, Venetiis, 1559; Lib. vii, De corde et 
 Arteriis, p. 177. Inter nos ventriculos septum adest, per quod fere omnes 
 existimant sanguini a dextro venti'iculo ad sinistrum, aditum patefieri ut fiat 
 facilius in transitu ob vitalium spiritum generationem tenaem reddi sed longa 
 errant via nam sanguis per arteriosam venam ad pulmonem fertur, ubique 
 attenuater deinde cum aere una per arteriam venalem ad sinistrum cordis 
 ventriculis defertur quod nemo hactenus aut animadvertit aut scriptum 
 reliquit licet maxime fit ab omnibus animadvertendem. 
 
 ^Tollin Die Entdeckung des Blutkreislaufs, etc., Jena, 1876, p. 39. 
 
28 CIRCULATION OF THE BLOOD. 
 
 authority in physiological matters, he would respect him equally in 
 reference to theological ones. Whether Colombo was acquainted 
 with the writings or the views of Servetus may be a question, 
 but there can be no doubt that he understood and described the 
 pulmonary circulation. This able anatomist, however, held 
 entirely erroneous views as regards the general or systemic circu- 
 lation, for, in speaking of the liver and veins, in the same work 
 that we have just referred to, he distinctly states that the liver 
 is the head, the fountain, the origin of all the veins.* It is 
 evident that one who held, with Galen, that the veins originated 
 in the liver, the venous blood being transmitted thence to the 
 periphery, could have no idea of the general circulation. 
 
 In 1571, eighteen years after the death of Servetus, there 
 appeared the Qusestionum Peripateticarum of Csesalpinus, one 
 of the most distinguished of the many Celebrated men that Italy 
 produced in the 16th century. Csesalpinus taught medicine at 
 Pisa, and was afterwards physician to Pope Clement VIII, at 
 Rome, and was as distinguished a botanist as a physician, being 
 the first to classify plants according to a natural method, and 
 may be justly regarded as the father of vegetable anatomy. It 
 is an interesting fact that in this work, in which the pulmonary 
 circulation is described, for the first time in the literature of 
 medicine the term circulation of the blood is used, Csesalpinus 
 saying^ that this circulation of the blood from the right ventricle 
 
 'De jecore etvenis,p. 164, op. cit. Aliqui credidere ibi generavi spiritus 
 naturalis quam tamen sententia non approbo membrum est sanguini facationi 
 dioatum neg enim sanguis alibi gignitur quioquid de corde scripserit Peripa- 
 teticoni princeps Aristol. Est igitur jecur omnium venarum caput fons 
 origo radix huius cava parte vena oritur selechia a Grseois quam portam 
 Latinii dicunt. 
 
 ''Andrea Ccesalpini Areiini Qucestionum Peripateticarum, Venetiis, 1593, 
 
CIRCULATION OP THE BLOOD. 29 
 
 of the heart, by the lungs, to the left ventricle of the same, agrees 
 best with what appears from dissection. One can hardly believe 
 that sucli a learned man as Csesalpinus was unaware of the views 
 of Servetus or Colombo; certainly, at least, of the existence of 
 the De re Anatomica, published so recently as 1559, and by an 
 anatomist who taught in the neighboring city of Padua ; and yet 
 he mentions neither. 
 
 If, however, Csesalpinus was indebted to Servetus for his views 
 of the pulmonary circulation, he had the same good reason as 
 Colombo for not mentioning him, and no particular reason for 
 referring to Colombo. It is strange, however, that if Csesalpinus' 
 views upon the pulmonary circulation were derived from either 
 the works of Servetus or Colombo, he should have held, with 
 Galen, as he undoubtedly did,* that the septum of the heart was 
 pervious, part of the blood passing directly from the right to the 
 left ventricle, which both Servetus and Colombo showed was 
 not the case. Had Ca3salpinus published nothing more than 
 his Qusestiorum Peripateticarium, there would have been no 
 
 Lib. V, Qucestio iiii, p. 125. Id circo pulmo per venam arteriis similem ex 
 dextro cordis ventriculo semilem paurles sanguinem eumque per anastomo- 
 sum arterise venali reddens que in sinistra cordis ventrioulum rendit trans- 
 missio internam aere frigldo per asperse arterise canales qui juxta arteriam 
 venalem protenditur non tamen osculis oommunicantes ut putant Galenus 
 solo tacto imperat. Huic sanguinis circulatione ex dextra cordis ventriculo 
 per pulmones in sinistrum ejus dem ventriculem optime respondent ex quse 
 a dissectione apparet. Cum enim servere oporteret in corde sanguine ut 
 fieret alimenti perfeotio primo quidem in dextro ventriculo in quo crassior 
 adhuc continetur sanguis, deinde autem in sinistro ubi syncerior jam sanguis 
 est, partim per medium septum, partim per medios pulmones refrigerationis 
 gratia ex dextro in sinistrum transmittitur. 
 
 'Op. cit. p. 126. Sanguis partem per medium septum partem per medios 
 pulmones .... ex dextro in sinistro ventriculum cordis transmittitur. 
 
30 CIECULATION OF THE BLOOD. 
 
 necessity for my referring to that philosopher in connection with 
 the history of the discovery of the circulation of the blood. 
 Twelve years afterwards (1683), however, the De Plantis, by the 
 same author, appeared, and this work has the greatest interest for 
 us, as for the first time the general or systemic circulation, with 
 the exception of the capillaries, is described, though it must be 
 admitted that the description is very brief, and supported by 
 little or no experimental evidence. In this work Caesalpiniis 
 distinctly says^ that the food is carried by the veins to the heart, 
 and thence, by means of the arteries, is distributed to all parts 
 of the body. Csesalpinus not only understood the way in which 
 nutriment is distributed throughout the economy, but, with the 
 exception of the capillaries, the manner in which the blood flows 
 through the system. For in his Qusestionum Medicarum (p. 234), 
 Csesalpinus calls attention to the fact that when the veins in the 
 neck are compressed the swelling of the veins is between the 
 brain and ligature, not between the ligature and the heart, 
 and draws the conclusion that just the opposite ought to happen, 
 that is, the swelling ought to be between the ligature and the 
 heart, if the motion of the blood in the veins is from the 
 heart and other viscera to the periphery of the system, as was 
 the general opinion at that time. Csesalpinus continues, in the 
 same page, by saying that there is a perpetual motion of the 
 blood from the vena cava, through the heart and lungs, to 
 the aorta, and that the arteries communicate with the veins, by 
 
 ^De Plantis Libri. xvi Florentice, 1583, Lib. 1, Cap, ii, p. 3. Qua autem 
 ratione fiat alimenti attractio & nutritio in plantis consideremua. Nam in 
 anlmalibus videmus alimentum per venas duci ad cor tanquam ad officinam 
 caloris insiti adepta inibi ultima perfectione per arterias in universum corpus 
 distribue agente spiritu qui in eodem alimento in corde giguitur. 
 
CIRCULATION OF THE BLOOD. 31 
 
 what are called anastomoses ; that the blood flows to the upper 
 parts and returns, Euripus-like, to the lower ones, is perfectly- 
 evident, both when one is asleep and awake, and that this motion 
 is not obscure in any part of the body when you experiment by 
 binding veins or occluding them in any other manner. The 
 above distinct,, concise statements appear to me to prove that 
 Csesalpinus understood the systemic circulation, as far as was 
 possible for one who had never seen the capillaries; as regards 
 the pulmonary circulation he undoubtedly also states that the 
 blood passed from the right side of the heart to the left, by the 
 lungs; but as we have seen that, in the Qusestionum Peripateti- 
 carum, he says that part of the blood passes through the septum, 
 and as he does not contradict this statement, but refers to this 
 work as containing his views, he could only have understood 
 the pulmonary circulation imperfectly. By most of those who 
 have written on the discovery of the circulation, a very different 
 interpretation, however, is offered of the views of Csesalpinus 
 from that just given. By such, it is stated that Csesalpinus held 
 that there was a to-and-fro motion of the blood in the veins, 
 Euripus-like; that the arteries communicated with the veins 
 only during sleep; that the blood only irrigated the tissues, but 
 did not circulate through them, etc. If these are the views of 
 Csesalpinus, then he certainly did not understand the circulation 
 in any part of its course. 
 
 In order that the reader may judge for himself, as to what the 
 views of Csesalpinus really were, I will give the passage from 
 his Qusestionum Medicarum, — to which I have referred, both 
 in the original and in a translation — and will say but a word 
 further concerning it. 
 
 AndreoB Ccesalpini Aretini, Qumstionum Medicanum, Libri II, 
 
32 CIRCULATION OF THE BLOOD. 
 
 Venetiis, 1593, Liber Secundus, Qucest. xvii, pp. 233 et 234. — 
 "Ex hac vero positione non minum aliquando solum soporem 
 gigni ex venarurn apprehensione in collo, aliquando etiam suffo- 
 cationem. Necesse enim est ex ea apprehensione virtutem cordis 
 non communicari cerebro, ideo toUi sensum et motum voluuta- 
 rium toti corpori, at non est necesse oppleri adeo pulmonem, ut 
 suffocetur. Sed illud speculatione dignum videtur, propter quid 
 ex vinculo intumescunt vense ultra locum apprehensum, non 
 citra; quod experimento sciunt qui venam secant, vinculum enim 
 adhibent citra locum sectionis non ultra, quia tument vense ultra 
 vinculum non citra. Debuisset autem opposito modo contingere, 
 si motus sanguinis et spiritus a visceribus fit in totum corpus — 
 intercepto snim meatu non ultro datur progressus, tumor igitur 
 venarum citra vinculum debuisset fieri. Au soliutur dubitatio 
 ex eo quod scribit Aristoteles de som Cap. 3, ubi inquit Necesse 
 euim quod evaporatur aliquo usque impelli, delude convert! &c. 
 permntari sicut Euripi, calidura enim cuiusque animalium ad 
 superiora natum est ferri, cum autem in superioribus locis fuerit, 
 multu simul iterum revertitur, fertur que deorsum. Heec Aris- 
 toteles. Pro cuius loci explicatione illud sciendum est, Cordis 
 meatus ita a natura paratos esse, ut ex vena cava introraisio fiat 
 in cordis ventriculum dextrum, unde patet exitus in pulmonem. 
 Ex pulmone prseterea alium ingressum esse in cordis ventriculum 
 siuistram, ex quo tandem patet exitus in arteriam. Aortam, 
 membranis quibus dam ad ostia vasorum appositis, ut impediant 
 retroeessum sic enim perpetuus quidam motus est ex vena cava 
 per cor et pulmones in arteriam Aortam, ut in qusestionibus 
 peripateticis explicavimus. Cum autem in vigilia motus caloris 
 nativi fiat extra scilicet ad sensoria, in somno autem intra, scilicet 
 ad cor, putandum est in vigilia multum spiritus et sanguinis ferri 
 
CIRCULATION OP THE BLOOD. 33 
 
 ad arterias, inde enim in nervos est iter. In somno autem 
 eumdem calorem per venas reverti ad cor, non per arterias, 
 ingressus enim naturalis per venam cavam datur in cor non per 
 arteriam Indicio sunt pulsus, qui ex pergiscentibus fiunt magni, 
 vehementes, celeres, et crebri cum quodani vibratione, in somno 
 autem parvi, languidi, tardi et rari de can, pul 9 et 10. — Nam 
 in somno calor nativus minus vergit in arterias, in eosdem 
 erumpit vehementius, cum expergiscuntur. Vente autem con- 
 trario modo se iiabent, nam in somno fiunt tumidiores in vigilia 
 exiiiores ut patet intuenti eos qu9e in manu sunt. Transit enim 
 in somno color nativus ex arteriis in venas per osculorum com- 
 munionem quam anastomosin vocant & inde ad cor ut aute 
 sanguinis exundatio an auperiora &c. retrocessus ad inferiora 
 instar Euripi manifesta est in somno et vigilia, sic non obscurus 
 est burn modo motus in qua cunque parte corporis vinculum 
 adhibeatur aut alia ratione occludanter vense Cum enim toUitur 
 permeatio, intumescunt rivuli qua parte fluere solent. Forte 
 recurrit eo tempore sanguis ad principium ne intercisus extin- 
 guatur." 
 
 " Truly, from this proposition, it is not to be wondered at that 
 sometimes sleep alone is produced, by the seizure of the veins in 
 the neck, sometimes even suffocation. For it is necessary from 
 that seizure, that the power of the heart is not communicated to 
 the brain, so the consciousness and voluntary motion of the 
 whole body is taken away, but it is not necessary, for such an 
 effect, to fill the lungs to suffocation. But that appeal's worthy 
 of observation, for the reSson that the veins swell up from a 
 bandage on the other side of the seat of application, not this 
 (towards heart), which those know from experience who bleed, 
 for they apply the bandage this side of the position of section, 
 
34 CIRCULATION OF THE BLOOD. 
 
 not on the other side, because the veins-swell up on the other 
 side of the bandage, not this side. But the opposite way ought 
 to happen if the motion of the blood and spirit is made from 
 the viscera into the whole body^ for the canal being intercepted, 
 progression is not given, therefore, the swelling of the veins 
 ought to be made on this side of the bandage. Or, indeed, our 
 doubt is solved of that which Aristotle writes of sleep. Cap. 3, 
 where he says, Necessarily what is evaporated, impelled con- 
 tinually elsewhere, is then turned back and changed, like the 
 Euripus; for the heat of every animal is intended by nature to 
 be carried to the higher parts, much, at the same time, on the 
 other hand, is turned back and carried downward. So, Aristotle. 
 For the explanation of this passage we must know this. That 
 the cavities of the heart are so prepared by nature that there is 
 an opening made from the vena cava into the right ventricle of 
 the heart, whence an exit into the lungs is open. Further, from 
 the lungs there is another opening into the left ventricle of the 
 heart, from which, finally, an exit is open into the arterial aorta, 
 the valves of which are placed at the mouths of the vessels, in 
 order to impede retrogression. For thus there is a perpetual 
 motion from the vena cava, through the heart and lungs, to the 
 arterial aorta, as we have explained in the peripatetic questions. 
 But since, when we are awake, the motion of the native heat is 
 outwards, that is, towards the sensorium, but in sleep inwards, 
 that is, towards the heart, we must be led to think that while we 
 are awake much spirit and blood are carried to the arteries, for 
 thence is the way to the nerves. But in sleep the same heat 
 reverts, by the veins, to the heart, not by the arteries, for the 
 natural entrance to the heart is given by the vena cava, not by 
 the artery. The evidence of this is the pulses, which, while we 
 
CIRCULATION OF THE BLOOD. 35 
 
 are awake, are made great, vehement, rapid, swift, with each 
 vibration, but in sleep small, languid, slow, infrequent (3 de can. 
 pul. 9 and 10). For in sleep the native heat tends less towards 
 the arteries, it bursts forth into the same most vehemently when 
 they are awake. But the veins have a contrary habit, for in 
 sleep they become more swollen, and when we are awake more 
 empty, as is evident by observing those which are in the hand. 
 For the native heat, in sleep, passes from the arteries to the 
 veins by their common mouths, which they call anastomoses, and 
 thence to the heart. But the pouring out of the blood to the 
 higher parts and its retrocession to the inferior ones, like that of 
 the Euripus, is manifest in sleep, and when we are awake, for 
 this kind of motion is not obscure in whatever part of the body 
 the bandage is applied, or by whatever other means the veins are 
 closed up. For when the permeation is allowed, the rivulets 
 swell up in the parts by which they are accustomed to flow. The 
 blood recurs powerfully at that time to its source, lest, having 
 been cut oiF, it be extinguished." 
 
 It will be observed that in this passage the word Euripus 
 occurs twice. In the first instance, however, it is Aristotle that 
 uses it, ex{)ressing by it in a metaphorical way, his view as to 
 the ebb and flow of the heat of an animal; Euripus being a 
 narrow sea between Bceotia and Eubcea, which, according to the 
 ancients, ebbed and flowed several times a day. Hence, we find 
 several writers using the word Euripus to express an oscillation 
 of any kind. As we are not concerned at present with what 
 Aristotle or Csesalpinus thought of animal heat, it is not neces- 
 sary to dwell further upon this part of the passage, simply 
 mentioning that Csesalpinus says nothing as regards the heat as 
 evidenced by the pulse, etc., which is inconsistent with what is 
 
36 CIRCULATION OP THE BLOOD. 
 
 known at the present day, the heat going to the heart by the 
 veins, not by the arteries. In the second instance where the 
 word Euripus occurs, Csesalpinus uses it metaphorically, in the 
 sense of an oscillation; but in this case, as applied to the blood. 
 It is distinctly stated that the blood is poured out towards the 
 superior parts, and retrogrades to the inferior ones, both asleep 
 and awake. The ebb and flow is from the heart to the head 
 and back again, by the arteries to the head, by the veins to the 
 heart, there being a perpetual motion from the vena cava to the 
 heart, through the lungs back to the heart, and so to the arteries; 
 thence the way to the nerves, the nerves being nourished by 
 arterial blood, like all the other structures. Not a word is said 
 of there being an ebb and flow, a Euripus-like motion, in the 
 veins; on the contrary, it is distinctly said that the blood flows 
 in the veins towards the heart, as can be proved by binding up 
 a vein anywhere. It will be observed that Csesalpinus says that 
 the natural heat passes, only during sleep, from the arteries to 
 the veins, by anastomoses. This statement, however, is a totally 
 different one from saying that the arteries anastomose only with 
 the veins during sleep. If there are anastomoses during sleep, 
 there are anastomoses during the wakeful condition. More heat 
 may be generated and transmitted through the economy at one 
 time than another, but the absence of all heat would not affect 
 the existence of the anastomoses. Csesalpinus, so far from say- 
 ing that the blood passes from the arteries to the veins o; ly 
 during sleep, says that the motion of the blood is perpetual, 
 during both the sleeping and waking conditions. That Csesal- 
 pinus understood that the blood circulated, and did not simply 
 irrigate the system, seems to be proved by the fact of his saying 
 that the blood circulates in one work, in another that the blood 
 
CIRCULATION OF THE BLOOD. 37 
 
 is carried by the veins to the heart, and from the heart by the 
 arteries, and that the arteries anastomose with the veins, and that 
 the motion is perpetual from the vena cava to the heart and 
 lungs to the aorta. It is not to be implied, however, that he 
 understood the exact manner in which the blood passed from 
 the arteries to the veins because he uses the word anastomoses. 
 Galen and Servetus used the same word in this connection, as 
 also afterwards Harvey, and yet there is no reason to suppose 
 that these writers ever meant, by the word anastomosis, the 
 capillaries, and yet, without a knowledge of these vessels, the 
 systemic, no more than the pulmonary circulation, could be 
 thoroughly understood. 
 
 It has been stated that Moreri [Le Grand Diot. Hist., Paris, 
 1732, Vol. II, p. 675) was the first to claim for Csesalpinus the 
 honor of the discovery of the circulation. This is incorrect, 
 however, as Douglas, in his Bibliographice Anatomioce, after 
 paying a proper tribute to Harvey, observes that it is to be 
 regretted that Csesalpinus did not expose his views more fully. 
 N"evertheless, that he (Ceesalpinus) who invented is as deserving 
 of honor as he (Harvey) who perfected. 
 
 Bibliographice Anatomies, Jacobi Douglas, Londini, 1715, p. 
 140. "Et licet ffelicissimusAngliffiadeo magnum anatomias lumen 
 terrarum orbi offerenti medullitus congratuler, dolere tamen est, 
 Csesalpinum quse perspicue satis nullisque verborum ambagibus 
 intricata tradit non raagis encoluisse & in Hypothesin generi 
 humano profuturam perduxisse, nihilominus par decus manet 
 & ilium qui primum invenit & qui postremum perfecit, nescio 
 euim an prsestat invenisse an detasse." 
 
 It will be seen, from this brief r6sum6 of the views of Ser- 
 vetus, Colombo and Csesalpinus, that while the pulmonary circu- 
 
38 ciecuIjAtion of the blood. 
 
 lation (with the exception of the capillaries) was understood by 
 Servetus and Colombo, they had but little or no idea of the 
 general or systemic circulation; on the other hand, while the 
 general circulation (with the exception of the capillaries) was 
 correctly described by Csesalpinus, he understood the pulmonary 
 circulation only imperfectly. Throughout this lecture I use the 
 terms pulmonary and systemic circulations in their conventional 
 sense; but both these terms are incorrect and misleading, since 
 the blood after leaving the left ventricle does not return at once 
 to the right side of the heart, which would constitute a pulmo- 
 nary circulation, but first passes through the system, and, having 
 passed through the system, it does not directly return to the left 
 ventricle, a systemic circulation, but passes through the heart 
 and lungs first. There is, therefore, but one circulation. But 
 this is only true in a certain sense, as the blood, after leaving 
 the heart, may go to the head or the extremities, etc., and then 
 return to the heart. As a matter of fact there are, therefore, 
 innumerable circulations. It cannot be said, therefore, that any 
 one, up to the end of the 16th century, understood the entire 
 circulation of the blood, using the word circulation in the sense 
 that we do at the present day. Isolated portions of the circula- 
 tion only had been described. It remained now for some one to 
 show the connection between the facts already established, to 
 add important new ones, to offer a view based upon observation 
 and experiment that would explain all the facts. In a word, to 
 demonstrate that the blood actually circulates. 
 
 It is claimed by some writers that this honor should be 
 accorded to Carlo Rumi,/of Bologna, it having been asserted 
 that Rumi discovered both the pulmonary and systemic circu- 
 lations. Even if Rumi had described both the circulations 
 
CIRCULATION OF THE BLOOD. 39 
 
 correctly, that would not have entitled him to have been called 
 their discoverer, since the pulmonary circulation had been previ- 
 ously describe by Servetus and Colombo, and the systemic circu- 
 lation by Csesalpinus. Rami does not appear to me, however, 
 to have thoroughly understood either the systemic or pulmonary 
 circulations, since he states the veins carry the nourishment, as 
 well as the arteries, to the viscera, and that the pulmonary 
 arteries nourish the lungs. There can be no possible misunder- 
 standing of Rumi's views as to the systemic circulation, us in 
 his Anatomia del Cavallo, in Venetia, 1599 (Lib. I, p. 65), he 
 says, "la vena che porta nutrimento allochio" (the vein that 
 carries nutriment to the eye), and gives a figure (Tav. II, Fig. 
 vii) illustrating this view. At p. 94, in speaking of the arteries 
 and veins, we find, "che paiono esser fatte solamente per portar 
 nodrimento a parte cosi nobile, come la spinal medolla," that 
 appear to be made solely to carry nutriment to parts as noble as 
 the spinal medulla; and at p. 100, they give nutriment, life and 
 motion to all these parts, — a branch of the vein and artery 
 "Danno nutrimento, vita, et moto a tutte queste parti, un ramo 
 delia vena et arteria." That Rumi had but an imperfect idea 
 of the pulmonary circulation is evident from the manner in 
 which he describes it, p. 108 : — 
 
 "L'officio di questi ventricoli, e del diritto disponere il sangue, 
 che di quello si possano generare li spiriti della vita, et nodrire 
 i polomoni ; del sinistro e ricever questo sangue gia disposto, et 
 convertirne una parte ne gli spiriti, che danno la vita et mandare 
 il restante insieme con quelli spiriti, per I'arterie, a tutte le parti 
 del corpo Nell uno et nellaltro ventriculo, sono due bocche 
 o pertugi per quelli del diritto entra il sangue della vena grande, 
 cava et esce per la vena arteriale et per quelli del ventricolo 
 
40 CIRCULATION OF THE BLOOD. 
 
 manco entra il sangue accompagnato dall aere preparato tiei i 
 polmoni per I'arteria venale il quale fatto tutto spirituoso, e per- 
 fettissimo vel ventricolo sinistro esce (guidato dall arteria grande) 
 per tutte le parti del corpo eccetto che per li polmoni per farle 
 partecipe di qiialche calore, che li da la vita." 
 
 " The office of these ventricles is, for the right one, to prepare 
 the blood, that the spirits of life can be generated from it and 
 the lungs nourished; of the left, to receive this blood already 
 prepared, and to convert a part into spirits, which give life, and 
 to send the rest, together with the spirits, by means of the 
 arteries, to all parts of the body. In both the ventricles are 
 two mouths or chinks; by that of the right the blood of the 
 great vein, or cava, enters, and goes out by the arterial vein; by 
 that of the left ventricle, the blood enters, accompanied by the 
 air prepared in the lungs from the venous artery; this being 
 entirely spiritualized and perfected in the left ventricle, goes out 
 (guided by the great arteria) through all parts of the body, 
 except that for the lungs, to impart it that heat which gives 
 life." 
 
 During the middle of the 16th century the fame of the 
 medical schools of Italy had spread far and wide. Students 
 from all parts of Europe crowded to listen to the eloquent 
 lectures of Vesalius, Eustachius and Fallopius, to attend 
 the anatomical demonstrations given in the amphitheatres at 
 Padua, Pisa and Bologna. At the end of the 16th century, 
 with other foreigners, William Harvey came to Padua and 
 studied with the celebrated Fabricius, of Aquapendente, the first 
 anatomist to thoroughly describe, in his " De venarum ostiolis, 
 Patav, 1603," the valves in the veins.^ Fabricius is often said 
 
 ^Hieronymi Fabrici ab Aquapendente Opera Omnia Lipsice, 1687, De 
 
CIRCULATION OF THE BLOOD. 41 
 
 to have been the first to have discovered these valves; indeed, 
 he says so himself; but the presence of valves in the veins had 
 been previously noticed by several anatomists; among others, by 
 Cannanus,^ Sylvius,^ Eustachius' and Piccolhominus.* At this 
 
 Venarum Ostiolis, p. 150. " Sed neque aliquis prius hsec viderit quam Anno 
 Domini septuagesimo quarto supra millesimum et quingentessimum quo a 
 me summa Isetitia inter dissecandum observata fuere." 
 
 'Amati Lusitani Medici Physici Prsestantio Curationum Medicinalium, 
 Lugduni, 1567. In this work, p. 271, Lusitanus mentions having demon- 
 strated the valves in the azygos vein in man and in animals, at Perrara, in 
 1547; and refers to Cannanus as having previously noticed them also: " nam 
 anno 1547, Ferrariae, duodecim corpora humana brutorun disseeare fecimus 
 in omnibus ita evenisse magna doctorum hominum spectante coucione 
 videmus ut itidem quoque adnotabat Joanus Baptista Cannanus admirandus 
 anatomicns. ' ' 
 
 ^In Hippocrates et Galeni Physiologise partem anatomicam Isagoge a 
 Jacobo Sylvio-Parisiis, 1555. In Cap. mi, p. 17, of this work, Sylvius 
 refers to the valves in the azygos, brachial, crural, etc., veins, considering 
 that they act like those closing the mouths of the cardiac vessels : "Mem- 
 branse quoque epiphysis est in ore venae azygi, vasorum que aliorum mag- 
 norum sepe ut jugularium, braohialium, cruralium trunco cavse ex hepate 
 profiliensis usus euisdem cum membranis ora vasorum cordis claudentibus." 
 
 ' Bartholmsei Eustaohii Opuscula Anatomica Venetiis, 1584. Bustachius, 
 in his work, De Vena Sine Pari, p. 289, after describing the valve named 
 after him, refers to the valves in the coronary veins: "pariter atque ilia 
 quam orificio vense coronarise praefici dixi, quasi cornutae lunse speciem refert, 
 aliquando adeo parva et augusta est, ut nisi diligenter animum quis advertat, 
 quasi nulla sit praetereatur. " 
 
 ^Anatomicae Prselectiones Archangel Piccolhomini Romae, 1586. . Accord- ■ 
 ing to Piccolhominns, the excitement of the discovery of the valves in the 
 veins threw him almost in ecstaoy. At p. 412 he observes : " Unum solum 
 eis addere volo magni momenti ab omnibus praetermissum quod mihi summam 
 admirationem quum illud comperi ita excitant ut fere in exstasium ageret, 
 quod est in mediis venia recondltas esse innumerabiles pene valvas quemad 
 
42 CIECULATION Or THE BLOOD. 
 
 moment, however, that which interests us particularly in refer- 
 ence to these valves is, that Fabricius demonstrated them to 
 Harvey, and that the latter made such good use of that knowl- 
 edge that the names of pupil and master have ever since been 
 associated; for undoubtedly it was reflection upon what might 
 be the use of the valves, as well as other anatomical considera- 
 tions, that first led Harvey to investigate the manner in which 
 the blood flows through the system. Harvey studied about five 
 
 modom in orificiis vasorum cordis. Has venarum valvae maximae conspiouse 
 sunt in divisione ramorum vense cavEB, quarum aliae superne deorsum alias 
 inferne sursum spectant. Ex gr ubi vena cava diducitur in jugularem 
 externam et internam, ibi colloeatse jacent valvse superne deorsum spec- 
 tantes quem in usum et finein. — Hunc igitur in finem in superioribus venis 
 fabrasfactae sunt valvs superne deorsum speetantes, ne in deeubitu, con- 
 fertim sanguis in cerebrum impetat, mille cerebri affeotus praeternaturam 
 procreaturus. Similiter in inferioribus venis ex gr ubi vena cava bipartite 
 scinditur in tibias progressura, sunt collocatae valvae inferne sursum spee- 
 tantes. Ex quem in usum. Ne sanguis quum sit gravis et fluidus totus 
 repente procumbat in pedes, inferiores que partes." 
 
 By most writers the French anatomist, Btienne, is considered to have 
 described the valves in the veins even before Cannanus or Sylvius. — De dis- 
 seotione partium corporis humani libri tres a Carolo Stephauo. Parisiis, 1545. 
 Lib. II, Hepar, Cap. ix, p. 182 — " Porro autem ne sanguis qui elaboratur in 
 hepate interdum regurgitet facti sunt a natura quidam veluti exortus &c. 
 apophyses membranarum quae huius modi periculo obsint quemadmodum in 
 corde valvulae ad spiritus conservationem." By apophyses Etienne, how- 
 ever, probably refers not to valves, since there are none, at least in the 
 hepatic veins of man, but to the semilunar folds seen at the lower border of 
 the orifices of the hepatic veins, at their entrance into the vena cava. 
 
 By a few writers it has been said that the celebrated Italian, Father Paul 
 Sarpi, not only described the valves in the veins, but also discovered the 
 circulation of the blood ; and that Fabricius was indebted to Sarpi for his 
 knowledge of the valves. So far as I have been able to learn, this view 
 appears to rest on no better authority than such was the opinion of the Vene- 
 
CIRCULATION OF THE BLOOD. 43 
 
 years at Padua (1598-1602). Naturally, during that time he 
 became thoroughly acquainted, not only with the views of his 
 teachers, Fabricius, Rudio, etc., but also with those of Colombo, 
 and probably of Csesalpinus and others who had taught and written 
 concerning the manner iu which the blood was supposed to flow. 
 Perfectly familiar with the anatomical views and methods of the 
 school of Padua, dissatisfied with the prevailing imperfect physio- 
 
 tian, Father Fulgentius, and of Peiresc, Senator of Aix. In a letter, written 
 from Pavia, October 30th, 1642, to Walaeus, Professor in Leyden, by Bartho- 
 linus, the latter states that, apropos of the Harveian circulation, Vesling had 
 told him a secret, to be revealed to no one, namely, that it was Sarpi who had 
 discovered the circulation and demonstrated the valves to Fabricius, and 
 that Sarpi's views were contained in his manuscript preserved at Venice, by 
 his disciple, Fulgentius. — Thomas Bartholinus Epistolse Hafniae, 1663, cent i, 
 epist XXVI — " De circulatione Harveyana secretum mihi aperuit Veslingius 
 nuUi revelandum ; esse nempe inventum Patris Pauli Veneti (a quo de 
 ostiolis venarum sua habuit Aquapendente) ut ex ipsius autographo vidit, 
 quod Venetiis servat P. Fulgentius, illius discipulus et successor." 
 
 In his life of Peiresc, Gassendi observes, in speaking to Peiresc of the 
 remarkable work of Harvey, on the circulation, recently published, that he 
 had mentioned to Peiresc that Harvey lay great stress upon the valves in the 
 veins as a proof of the circulation, and that Peiresc had heard something 
 about these valves from Fabricius, and remembered that Sarpi had discovered 
 them. 
 
 Viri Illustris Nicolai Claudii Pabricii de Peiresc Senatoris Aquis extiensis 
 Vita. Hagae Comitis, 1651, per Petrum Gassendum, p. 323. 
 
 "Cum simul monuissem Gulielmum Harvaeum Medicum Anglum, edidisse 
 prseclarum librum de successione sanguinis ex venis in arterias, & ex arterias 
 rursus in venas, per imperceptas; anastomoseis inter csetera vero argumenta 
 confirmasse illam ex venarum valvulis de quibus ipse inaudierat aliquid ab 
 Aquapendente, &c quarum inventorem primum Sarpium Servitam memi- 
 nerat; idco statim voluit & librum habere, & eas valvulas explorare, & alia 
 internoeere ; veluti maeandros mediastini cordis, quos Harvaeus est insiciatus, 
 et de quibus ipse fecerara securum. 
 
44 CIECULATION OF THE BLOOD. 
 
 logical theories of the circulation, on his return to England, 
 Harvey began anew the study of the flow of the blood. The 
 results of his reflection upon the knowledge gained in Italy, of his 
 studies on his return, by numerous vivisections, of extended com- 
 parisons of the structure of the heart and blood vessels in the 
 animal kingdom, of pathological observations upon man and beast, 
 were embodied in his classical treatise, "An Anatomical Exercise 
 on the Motion of the Heart and Blood in Animals."^ This 
 deservedly famous work will always serve as a model for physi- 
 ological investigation. Thus Harvey shows the necessity of 
 making vivisections^ in the study of the circulation, and too 
 much stress cannot be laid upon this statement, as it is often, 
 said that the circulation of the blood was discovered without 
 recourse to experiments upon living animals. The importance 
 of comparative anatomy as an aid to the study of physiology is 
 well shown by the use that Harvey made of his knowledge of 
 the structure and functions of the heart in the lower animals, in 
 his researches upon the circulation. Indeed, Harvey says,' had 
 anatomists only been as familiar with the dissection of the lower 
 animals as they are with that of the human body, matters that 
 have been a source of doubt would be free from all difficulty. 
 Unfortunately, comparative anatomy is too much neglected by 
 physiologists at the present day. That the value of pathological 
 anatomy in throwing light upon the normal functions of the body 
 was thoroughly appreciated by Harvey is evident from the cases 
 
 ' Exercitatio anatomica de motu cordis et sanguinis in aniraalibus. Franco 
 furti MDOXXViii. 
 
 ^Op. cit., Cap. II, p. 21, Ex vivorum diaaectione, etc. Cap. it, p. 25. 
 Motus cordis, etc , ex vivorum disseotione. 
 
 ' Cap. VI, p. 32. Quibua viis sanguis e vena cava in arterias. 
 
CIRCULATION OF THE BLOOD. 45 
 
 he refers to* in connection with his study of the circulation. 
 Harvey, therefore, did not confine himself to any one method 
 of investigation, but availed himself of vivisections, compara- 
 tive anatomy and pathology in his researches. It may be seen, 
 by referring to the writings of the great predecessors of Harvey, 
 that with the exception of Csesalpinus, it was always assumed 
 that the venous blood flowed from the viscera to the periphery. 
 Undoubtedly Harvey demonstrated far more thoroughly, by 
 experiment and argument, than Csesalpinus, the true course of 
 the venous blood, and this he proved in many different ways. 
 Thus, in his thirteenth chapter,^ after referring to the discovery 
 of the valves of the veins by Fabricius, and the different uses 
 that had been assigned to them, Harvey proceeds to show that 
 the valves are disposed in such a way that they only permit the 
 blood to pass through them in one direction, and that is towards 
 the heart,' demonstrating this by calling attention, as Csesalpinus 
 had done before him, to the condition of the veins when com- 
 pressed as if for bleeding. At intervals in the course of the veins, 
 under such circumstances, large knots are visible, which are due to 
 
 ' Cap. Ill, p. 34. Arteriarum motua qualis ex vivorum dissectione. 
 
 ^ Cap. xm, p. 54. Tertium suppositum confirmatur, etc. 
 
 ' It must not be forgotten, as may be seen from the quotation given at 
 p. 41, Note 4, that Pleoolhominus had already described the valves in the jugu- 
 lar vein as looking from above downward, and those in the veins in the extremi- 
 ties as looking from below upward, and drew the conclusion, from such dis- 
 position, that these valves prevented regurgitation to the head and extremi- 
 ties respectively. It is to be regretted that Harvey, in his description of the 
 valves and the flow of blood through the veins, should never have mentioned 
 either Piccolhominus or Csesalpinus, as it is probable that he was acquainted 
 with the writings of these anatomists, both teaching at Rome about the same 
 time. 
 
46 CIRCULATION OF THE BLOOD. 
 
 the distended valves which thus show themselves externally. By 
 pressing upon these veins above or below, or between the valves, 
 Harvey showed that the venous blood always passed in the same 
 direction, that is, toward the heart, and concluded that the functions 
 of the valves were like those of the semilunar valves of the pul- 
 monary artery and aorta, to prevent all reflux.' Excellent figures 
 are given in this chapter to illustrate the experiments by which 
 the functions of the valves were demonstrated. Further, that the 
 blood flowed towards the heart in the veins and from the heart in 
 the arteries, was beautifully demonstrated by an experiment upon 
 a living snake, so clearly described by Harvey in Chapter x. 
 After noticing the pulsating heart in the snake as it appeared 
 after the animal had been opened, Harvey calls attention to the 
 fact that if the vena cava be compressed it gradually empties 
 itself between the point of compression and the heart ; whereas, 
 if the aorta be compressed, it becomes distended between the 
 heart and the point of compression, showing conclusively that 
 the blood in the vena cava flows towards the heart, while that 
 in the aorta flows from the heart. In his second answer to 
 Kiolan, Harvey^ gives further proof of the circulation in notic- 
 ing that in a divided artery the blood flows from the end of 
 
 ^ The importance of the valves in the veins, either functionally or as leading 
 to the discovery of the circulation, must not be exaggerated, since in many 
 veins there are no valves. Thus in man, at least, however it may be in other 
 mammals, valves are not found in the vense cav£e, the innominate, pulmo- 
 nary, portal, hepatic, renal, uterine, ovarian, iliac, spinal, veins. Further, 
 there are few valves in the veins of birds, reptiles or fishes, and none in the 
 veins of the Invertebrata, and yet the blood circulates in all these animals. 
 It is evident, therefore, that the valves in the veins are not indispensable in 
 the maintenance of the circulation. 
 
 * Opera Omnia Edita, 1766, p. 120. Exercitatio altera ad J. Riolanum. 
 
CIRCULATION OF THE BLOOD. 47 
 
 the vessel that is still in connection with tlie heart, whereas 
 in the divided vein the blood flows from that part of the 
 vessel separated from the heart. One of the most remarkable 
 proofs of the circulation of the blood advanced by Harvey ^ 
 is, that more blood passes through the heart in a given time than 
 can be accounted for by the ingesta or by the quantity of the 
 blood in the vessels; hence the blood must pass and repass 
 through the heart, and in estimating the amount of blood flow- 
 ing from the left ventricle into the aorta during a short period 
 of time even, we necessarily count the same blood over and over 
 again. Harvey was not only the first to correctly describe the 
 entire circulation, but in the great work^ we have so often 
 referred to is found the first accurate account of the movements 
 of the heart, the successive dilations and contractions of the 
 auricles and ventricles, the contraction, hardening and elevation 
 of the heart against the chest, etc. An excellent description, as 
 may be supposed, is also given of the pulmonary circulation, etc. 
 Further, though from the days of Aristotle it was known that 
 there was some connection between the beating of the heart and 
 the pulse, Harvey' showed clearly that the dilatation of the 
 artery, or the pulse, was the effect of the contraction of the 
 ventricle. Harvey was not the first, however, to show this, 
 since in an ancient work, "Synopsis peri Sphugmon," by an 
 unknown author, the pulse in this respect was correctly described. 
 When this work was first discovered, according to D'Aremberg, 
 it was, without any reason, attributed to Rufus, of Ephesus. 
 The description I refer to is to be found at p. 20 : — 
 
 1 Cap. IX, p. 42. 
 
 2 Cap. II, m, IV, T, Ti. 
 
 ' Cap. Ill, p. 24, Arteriarum motus qualis ex vivorum disSectione. 
 
48 CIECITLATION OF THE BLOOD. 
 
 Suvo(piis xspt aipuyixio'j, Traite sur le Pouls attribue a Eufus 
 d'Ephese, par le Dr. Ch. Daremberg, Paris, 1846, p. 20. — U5)<s 
 
 ■fi-jerai aipufiuxi; Ti'jtrai de atpuyiJ.ii's ourwg. 'Hxapdia Szav i-Kia-d- 
 atTai ix TOO ■Kvsujj.moi; to -nnedna nptuTfj abrb ds^srai el? ttjv apiarepav 
 auTrji xoikiaVj slra k-KiauinttiTouiTa Ips^-^g auraT? raij a.pTijpiai<s i-c^o- 
 pijj'eT. Su/j-jSali/ei 00,/, ii:\ /isv riji ao[i.T:T(biTeiu<s liXyjpou/xiviuv rmv hj tu) 
 au>;j.aTi apTyjpiB'j rdv <T(puy[j.bv aTZOTiksTaf^ai^ xevou/iivtuv de rr/v auaroXrqv 
 al fxh oZ'j dpTTjplai, zai>a>? eT/rov, rdv (Tpuy/xdv aTiorsXuuat TzXrjpouiisvat 
 xal Ss-j^oiiivai ro Trvsu/ia, rj 8s xapSia xsvoufiivrj zai?u)? ifij? uitodsiSofiev. 
 
 "How is the pulse generated? The pulse is produced as 
 follows : The heart, after having drawn iu the air from the lung, 
 first receives it in its left cavity, then falling back upon itself 
 immediately distributes it to the arteries ; it follows, then, that, 
 during the collapse of the heart, the arteries of the body being 
 filled, their pulse is produced, and when empty, their systole. 
 As I say, the pulse is produced in the arteries when full and 
 receiving the air, and in the heart when empty, as we establish 
 below." 
 
 In his view of the contraction of the ventricle being the cause 
 of the dilation of the artery, Harvey was ' anticipated also in 
 modern times by Csesalpinus, who observes in his Qusestionum 
 Peripateticarum, 1593, Lib. Quint, Qusest. iiii, p. 122, that " it 
 happens that when the heart is contracting, the arteries are 
 dilated, and it dilating, are contracted." 
 
 " Cum enim vasorum in cor definentium qusedam intromittant 
 contentam in ipsis substantiam, ut vena cava in dextro ventrieulo 
 & Arteria venalis in sinistro qusedam educant, ut arteria aorta in 
 sinistro ventrieulo et vena arterialis pulmonem nutriens in dextro, 
 omnibus autem membranulfe sint appositse ei officio delegatse ut 
 oscula intromittentia non educant & educentia non intromittant. 
 
CIECULATION OF THE BLOOD. 49 
 
 continget corde contrapente se arterias dilatari & dilatante con- 
 stringi, non simul ut apparet." 
 
 For, on account of the vessels ending in the heart, some pour 
 their contents into its substance, as the vena cava into the right 
 ventricle and venous artery (pulmonary vein) into the left ; some 
 draw out, as the arterial aorta, from the left ventricle, and the arte- 
 rial vein (pulmonary artery), nourishing'^ the lungs from the right, 
 but in all are valves placed and adapted to that use that their 
 mouths, allowing to enter, do not lead out again, and those lead- 
 ing out to do not allow to enter again; it so happens that, the 
 heart contracting, the arteries are dilated, and dilating, contracted, 
 not at once, as appears. 
 
 I might dwell further upon the numerous observations, 
 demonstrations^ arguments based upon vivisections, comparative 
 anatomy, pathology, etc., to be found in Harvey's work. The 
 above brief descriptions will suffice, however, in giving an 
 idea of the general methods of investigation and the results 
 accomplished. The proofs advanced by Harvey were so numer- 
 ous and convincing as to render the conclusion that the blood 
 circulates inevitable. It was the only theory that would explain 
 all the facts, the only view that enabled one to sift the truth 
 from the error in the theories tfiat had been advanced before 
 Harvey's time. There is no doubt that Harvey was the first 
 to teach that the blood flows from the right side of the heart 
 through the lungs back to the left side of the heart, thence 
 into the aorta and arteries throughout the body, from the 
 arteries into the veins, returning by the veins to the heart 
 
 * It will be observed, from Csesalpinus referring to the pulmonary artery 
 being nutritive, that, as already mentioned, he did not understand the pulmo- 
 nary circulation. 
 
50 ciECULATio^r or the blood. 
 
 again — in a word, that he was the first to thoroughly describe 
 the entire circulation; but it must be admitted that he did not 
 demonstrate it, for there is no reason to suppose that Harvey 
 ever understood exactly, still less demonstrated, the manner in 
 which the blood flows from the arteries into the veins, since the 
 capillaries were not discovered till after his death. 
 
 With the discovery of the capillaries by Malpighi and Leeu- 
 wenhoek the entire circulation was for the first time demon- 
 strated. That Harvey did not understand the manner in which 
 the blood flowed from the arteries into the veins is evident from 
 his own description. His words* are: Signum est, etc., san- 
 guinem ab arteriis in venas et non contra permeare et aut anasto- 
 mosis vasorum esse aut porositates carnis et partium solidarum 
 pervias sanguini esse" — that it "is obvious that the blood passes 
 from the arteries into the veins, etc., and not the contrary; and 
 that there are either anastomoses of the vessels or porosities of 
 the flesh and solid parts that are pervious to the blood." Had 
 Harvey ever seen the capillaries, or even had an idea of their 
 structure, you may be assured that his description would have 
 been a graphic one. There would have been no obscurity in 
 reference to such an all important matter. That Harvey means 
 by the word porositates, porosities or holes, and not capillaries, 
 is evident from the way in which he uses this word in the intro- 
 duction to the Exercitatio, where, in speaking of the theory of 
 the ancients as regards the transmission of the blood through 
 the septum of the heart, he says they hold "that there are 
 numerous porositates in the septum of the heart, adapted for the 
 transmission of the blood; but, by Hercules, there are no porosi- 
 tates, neither can they be demonstrated" — "in septo cordis 
 ' Cap. XI, p. 48, Secundum auppositum Confirmatur. 
 
CIRCULATION OF THE BLOOD. 51 
 
 porositates pleures esse producendo sanguini accommodatas. 
 Sed me hercule porositates nullae sunt necque demonstrari 
 possunt." — Prooemium, p. 18. If by porositates Harvey means 
 capillaries, he would deny, then, that there are any capillaries in 
 the septum of the heart. Harvey appears to me to use the word 
 porositates just in the same sense (that of holes or porosities) 
 as used, as we have seen, by De Carpi, Vesalius, etc., in their 
 description of the septum of the heart. As regards the word 
 auastomoses, Servetus and Csesalpinus speak of the arteries 
 passing into the veins by anastomoses, and there is no more 
 reason for supposing that Harvey understood by this word 
 capillaries, than that they did. As an expression of the general 
 opinion at that time, about this matter, I will mention, inci- 
 dentally, that Wotton* observes: "There was one thing still 
 wanting to complete this theory, and that was the knowledge 
 how the veins received that blood which the arteries discharged. 
 This put them upon imagining that the blood oozes out of the 
 arteries and is absorbed by the veins, whose small orifices receive 
 it (which opinion has been generally received by most anatomists 
 since Dr. Harvey's time). (But Monsieur Leeuwenhoek has 
 lately found in several sorts of fishes, which were more manage- 
 able by his glasses, that arteries and veins are really continued 
 syphons wound about each other towards their extremities, in 
 numberless mazes, over all the body)." 
 
 In a very learned and critical article that appeared in the 
 American Journal of the Medical Sciences, for April, 1878, Dr. 
 Wm. S. Forbes endeavored to show that the word porositates 
 should be translated thin-walled vessels or capillaries. The 
 point to be determined is not how porositates ought to be trans- 
 ' Eeflectiona, etc., p. 235. 
 
52 CIRCULATION OF THE BLOOD. 
 
 lated, but what idea Harvey meant to convey by the use of 
 this word. Even admitting, which I do not, that by porosi- 
 tates Harvey meant capillaries, there is no reason to believe that 
 Harvey ever had seen these "thin-walled vessels," and without 
 demonstrating the capillaries the entire circulation cannot be 
 proved. 
 
 For the discovery of the capillaries, in 1661, science is in- 
 debted to Malpighi.^ In examining the lung of a living frog, 
 by means of the microscope, this distinguished physiologist ac- 
 tually saw the blood passing from the arteries into the veins by 
 means of extremely delicate tubes, at once the terminal branches 
 of the arteries and the beginnings of the veins. These minute 
 intermediate connecting tubes, the capillaries, were also seen by 
 Malpighi in the mesentery of the living frog as well as in the 
 lung. Some time after Malpighi's discovery, the capillary cir- 
 culation was observed by Leeuwenhoek.^ (1688), the Dutch 
 naturalist, with a microscope, in the lung of a bat, in the tad- 
 pole's tail, and in the fin of different kinds of fish. From that 
 tiime forward, the magnificent spectacle of the capillary circula- 
 tion became with microscopists a favorite subject for popular 
 demonstrations. Between 1628, the epoch of the appearance of 
 the " De motu cordis" of Harvey, and 1661, the year of the 
 discovery of the capillaries by Malpighi, our knowledge of the 
 circulation was extended by the discovery of the lacteals, etc. 
 Obviously, without a knowledge of the lymphatic system, that 
 of the circulation of the blood would be far from complete. In 
 this connection, however, it will be only necessary to allude to 
 
 ^ Marcelli Malpighi, Opera Omnia, Lug. Bat., 1687. Tomus secundus De 
 Pulmonibus Bpistola ii, p. 328. 
 
 2 Arcan. Nat. Lugd. Bat., 1722, pp. 158, 163. 
 
CIRCULATION OF THE BLOOD. 53 
 
 the names of Eustachius, Asselli, Pecquet, Rudbeck, Bartholinus, 
 whose contributions to the discovery of the lymphatic system I 
 have already described in my lectures upon absorption. As 
 regards the history of the discovery of the foetal circulation, that 
 will be considered with the study of development. During the 
 17th century our knowledge of the exact manner in which the 
 blood flows to all parts of the economy was greatly extended by 
 the study of the vascular system, by means of injections. It is 
 true this method of investigation had been occasionally attempted 
 before this period, but with little success. It was not until 
 Ruysch^ had perfected the methods of Swammerdam and Home, 
 and had demonstrated, by his very perfect injections, the manner 
 in which the blood vessels are distributed through the tissues, 
 that this method of study became universal with anatomists. 
 It can be readily understood that when arteries, capillaries and 
 veins are filled with a colored injection, how much easier the 
 course of these vessels can be made out, with either scalpel or 
 microscope, than if these blood vessels were simply studied in 
 the state in which they are usually found in the body after 
 death. Indeed, one of the most striking demonstrations of the 
 continuity of the vascular system consists in injecting a fluid 
 into an artery until the fluid escapes by an opening made in the 
 vein. Further, during the 17th century, so fertile in discovery, 
 the first attempts were also made in the study of the circulation 
 of the invertebrata, Willis,^ for example, describing the results 
 of his researches upon the circulation of the oyster, lobster, etc. 
 
 ' For an account of Ruysch, see eloge, by Pontenelle, in Hist, de I'Acad. 
 Sciences, 1731, and Hyrtl, Lehrbuch der Anatomi6, 1881, p. 61. 
 
 - Willis' Works, translated by S. Pordage, London, 1684 : Of the Soul of 
 Brutes, Chap. 3d, pp. 10, 11, Tables ii, iii. 
 
64 CIECULATION OF THE BLOOD. 
 
 It is, however, only during the present century that physiolo- 
 gists have understood the circulation of the blood as it takes 
 place in the mollusca, artieulata, etc., the vascular system of 
 animals, like insects, crabs, spiders, oysters, snails, etc., differing 
 very much from that of man or the mammalia ; Milne Edwards, 
 more especially, having shown, among other peculiarities, for 
 example, that the interorganic spaces or lacunte play the part of 
 blood vessels in the invertebrata, as is the case in certain parts 
 of the body of vertebrates also. "Within the past twenty-five 
 years great advances have been made in extending our knowl- 
 edge of the circulation in other directions. Thus, by the intro- 
 duction of the graphic method of study, we have seen, by means 
 of kymographions, sphygmographs, cardiographs, etc., that we 
 can determine blood -pressure, the rapidity with which the blood 
 flows in the system, etc., while the discoveries of Bernard, 
 Brown-S6quard, Ludwig, etc., have shown us how local varia- 
 tions ii? the general circulation are due to the influence of the 
 vaso-motor nerves. 
 
 If our account has been a correct one, the history of the dis- 
 covery of the circulation, recapitulated, divides itself naturally 
 into a series of epoch-making periods — 
 
 1. The structure and functions of the valyes of the Heart. 
 Erasistratus, B. C. 304. 
 
 2. The Arteries carry blood during life, not air. Galen, A.D. 165. 
 
 3. The Pulmonary circulation. Servetus, 1563. 
 
 4. The Systemic circulation. Csesalpinus, 1593. 
 
 5. The Pulmonic and Systemic circulations. Harvey, 1628. 
 
 6. The Capillaries. Malpighi, 1661. 
 
 The history of the discovery of the circulation, like all other 
 great movements, social, political and scientific, illustrates the 
 
CIECULATION OF THE BLOOD. 55 
 
 profound truth that intellectual development is as surely a 
 growth regulated by law as the life of a plant or animal. That 
 no intellect, however magnificent, rises so above the conditions 
 of its environment as to make it doubtful, for a moment, but 
 that the discovery would have been made sooner or later, even 
 had the name with which it is usually associated never existed. 
 Every mind is the product of its age. All the circumstances 
 prove that intellectual Europe at the end of the 16th century 
 ■was ready to accept the circulation of the blood. Had tlie dis- 
 covery been made some centuries sooner it would have fallen 
 still-born. All Italy, at that period^ was alive with speculation, 
 hypothesis, theory, as to the manner in which the blood flowed 
 through the body, and above all, Padua. Let any one compare 
 the works of the great Italian anatomists and physiologists of 
 the 16th century, in their Latin or Italian dress, with the 
 admirable work of Harvey on the Circulation, in the original, 
 and not in an English translation, and he will be impressed 
 with the fact that the same mode of thought and expression 
 pervades both. In his methods of investigation, observation, 
 arguments, Harvey is essentially Italian. By birth an English- 
 man, in thought Italian, Harvey lived and died a student of 
 Padua. 
 
 The discovery of the circulation of the blood, as we learn 
 from this necessarily brief account, belongs, therefore, to no one 
 age, country or person. Its history, extending as it does over a 
 period of over 2000 years, would naturally suggest that the 
 subject would have attracted the attention of the great medical 
 minds of all time; and such we have seen to have been the 
 case. Far from the grandest generalization in the whole range 
 of biology being discovered in its entirety by one mind, we have 
 
56 CIRCULATION OF THE BLOOD. 
 
 seen how, little by little, it was gradually established by many 
 observers; that long intervals would elapse without any progress 
 being made, when suddenly some ancient error would be dissi- 
 pated and fade away in the light of advancing science. Such a 
 history ought to encourage every student, for however trivial 
 and unimportant his experiments or observations may appear at 
 the time, every new fact once well established will sooner or 
 later assume its appropriate place as a part of some future 
 generalization; the chain of facts leading to a great discovery 
 being united together like living things, each linked with those 
 that have passed away with those still to come. Discoveries 
 great in themselves have often borne no fruit at the time, falling 
 on barren soil, the human mind not being sufficiently developed 
 to appreciate them. With the progress of knowledge, however, 
 the significance of discoveries made often ages ago and long for- 
 gotten, become, in time, apparent to all. Truth, like the rays 
 of the rising sun, is perceived first by those whose minds soar 
 above the intellectual horizon of their day, but sooner or later 
 its genial influence is felt by their humble followers, by all alike, 
 all in good time.