Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/854

Rh ANATOMY [HISTORY. to render anatomical knowledge inore precise by repealed dissections, and to illustrate the obscure by researches on the structure of animals in general. In this manner he investigated the formation of the foetus, the structure of the oesophagus, stomach, and bowels, and the peculiarities of the eye, the ear, and the larynx. The discovery, however, on which his surest claims to eminence rest is that of the membranous folds, which he names valves, in the interior of veins. Several of these folds had been observed by Fcrnel, Sylvius, and Yesalius ; and in 1547 Cannani observed those of the vena azygos ; but no one appears to have offered any rational conjecture on their use, or to have traced them through the venous system at large, until Fabricius in 1574, upon this hypothesis, demonstrated the presence of these valvular folds in all the veins of the extremities. Fabricius, though succeeded by his pupil Julius Casserius of Placenza, may be regarded as the last of that illustrious line of anatomical teachers by whom the science was so successfully studied and taught in the universities of Italy. The discoveries which each made, and the errors which their successive labours rectified, tended gradually to give anatomy the character of a useful as well as an accurate science, and to pave the way for a discovery which, though not anatomical but physiological, is so intimately connected with correct knowledge of the shape and situation of parts, that it exercised the most powerful influence on the future progress of anatomical inquiry. This was the knowledge of the circular motion of the blood, a fact which, though obscurely conjectured by Aristotle, Nemesius, Mondino, and Berenger, and partially taught by Servetus, Colum bus, Cajsalpinus, and Fabricius, it was nevertheless re served to William Harvey fully and satisfactorily to demonstrate. Mondino believed that the blood proceeds from the heart to the lungs through the vena arterialis or pul monary artery, and that the aorta conveys the spirit into the blood through all parts of the body. This doctrine was adopted with little modification by Berenger, who further demonstrated the existence and operation of the tricuspid valves in the right ventricle, and of the sigmoid valves at the beginning of the pulmonary artery and aorta, and that there were only two ventricles separated by a solid impervious septum. These were afterwards described in greater detail by Vesalius, who neverthe less appears not to have been aware of the important use which might be made of this knowledge. It was the ervetus. Spaniard Michael Servet or Servetus (born in 1509 ; burnt in 1553), who in his treatise De Trinitatis Erroribus, published at Haguenau in 1531, first maintained the imperviousness of the septum, and the transition of the blood by what he terms an unknown route, namely, from the right ventricle by the vena arteriosa (pulmonary artery) to the lungs, and thence into the arteria venosa or pulmonary vein and left auricle and ventricle, from which, he adds afterwards, it is conveyed by the aorta to all parts of the body. 1 1 The passage of Servetus is so interesting that our readers may feel some curiosity in perusing it in the language of the author ; and it is not unimportant to remark that Servetus appears to have been led to think of the course of the blood by the desire of explaining the manner in which the animal spirits were supposed to be generated : &quot; Vitalis spiritus in sinistro cordis vcntriculo suam originem habet, juvantibus maxime pulmanibus ad ipsius perfectionem. Est spiritus tenuis, caloris vi elaboratus, flavo colore, ignea potentia, ut sit quasi ex puriore sanguine lucens, vapor substantiam continens aquoe, acris, et ignis. Generatur ex facta in pulmone commixtione inspirati aeris cum elaborate subtili sanguine, quern dexter ventriculus sinistro com- niunicat. Fit autem communicatio haac, non per parietem cordis medium, ut vulgo creditur, sed magno artificio a dextro cordis ventri- culo, longo per pulmones ductu agitatur sanguis subtilis ; a pulmonibus prscparatur, flavus efficitur, et a vena arteriosa in arteriam venosam trausfunditur. Delude in ips?. p.rteria venosa, inspirato aeri miscetur Though the leading outlines, not only of the pulmonary or small but even of the great circulation, were sketched thus early by one who, though a philosopher, was attached to the church, it was only in his work De Re Anatomica, published at Venice in 1559, that Columbus formally and distinctly announced the circular course of the blood as a discovery of his own ; and maintained, in addition to the imperviousness of the septum, the fact that the arteria venalis (pulmonary vein) contains, not air, but blood mixed with air brought from the lungs to the left ventricle of the heart, to be distributed through the body at large. Soon after, views still more complete of the small or 1570-9; pulmonary circulation were given by Andrew Csesalpinus of Arezzo, who not only maintained the analogy between the structure of the arterious vein or pulmonary artery and the aorta, and that between the venous artery or pulmonary veins and veins in general, but was the first to remark the swelling of veins below ligatures, and to infer from it a refluent motion of blood in these vessels. The discoveries of Araiizi and Eustachius in the vessels of the foetus tended at first to perplex and afterwards to elucidate some of these notions. At length it happened that, between Harvey the years 1598 and 1GOO, a young Englishman, William Harvey, pursuing his anatomical studies at Padua under Fabricius of Acquapendente, learnt from that anatomist the existence of the valves in the veins of the extremities, and xmdertook to ascertain the use of these valves by experimental inquiry. It is uncertain whether he learnt from the writings of Csesalpinus the fact observed by that author, of the tumescence of a vein below the ligature, but he could not fail to be aware, and indeed he shows that he was aware, of the small circulation as taught by Servetus and Columbus. Combining these facts already known, he, by a series of well-executed experiments, de monstrated clearly the existence, not only of the small, but of a general circulation from the left side of the heart by the aorta and its subdivisions, to the right side by the veins. This memorable truth was first announced in the year 1619. It belongs not to this place either to consider the arguments and facts by which Harvey defended his theory, or to notice the numerous assaults to which he was exposed, and the controversies in which his opponents wished to involve him. It is sufficient to say, that after the temporary ebullitions of spleen and envy had subsided, the doctrine of the circular motion of the blood was admitted by all enlightened and unprejudiced persons, and finally was universally adopted as affording the most satisfactory explanation of many facts in anatomical structure which were either misunderstood or entirely overlooked. The inquiries to which the investigation of the doctrine gave rise produced numerous researches on the shape and structure of the heart and its divisions, of the lungs, and of the blood-vessels and their distribution. Of this descrip tion were the researches of Nicolas Steno on the structure of the heart, the classical work of Pdchard Lower, the dissertation of Pechlin, the treatise of Vicussens, the et exspiratione a fuligrae expurgatur ; atque ita tandem a sinistro cordis ventriculo totum mixtum per diastolcn attrahitur, apta supellex, xit fiat spiritus vitalis. Quod ita per pulmones fiat communicatio et pr&paratio, docet conjunctio varia, et communicatio venae arteriosrc cum arteria venosa iu pulmonibus. Confirmat hoc magnitude insignis vence arteriosa?, quae nee talis nee tanta esset facta, nee tantam a corde ipso vim purissimi sanguinis in pulmones emitteret, ob solum eorum nutrimentum ; nee cor pulmonibus hac ratione serviret, cum prseser- tim antea in erubryone solerent pulmones ipsi aliunde nutriri, ob mem branulas illas sou valvulas cordis, usque ad horum nativita- tem ; ut docet Galenus, &c. Itaque ille spiritus a sinistro cordis ventriculo arterias totius corporis delude transfunditur, ita ut qui tenuior est, superiora petit, ubi magis elaboratur, priccipue in plexu retiformi, sub basi cerebri sito, ubi ex vitali fieri iucipit auimalis, ad propriam ratioualis animce rationem accedens.&quot; De T-rinitaU, lib. v.