During fmtal life, says he, this is sufficiently evident. Part of the blood passes directly from the right to the left auricle through the foramen ovale, whilst the rest is conveyed into the right ventricle, and by its contraction forced into the pulmonary artery, and so through the ductua arteriosus into the descending aorta ; for, as he observed, the luuge do not admit of its passage through them in the Retns. In the adult • new condition is introduced, namely the function of the lungs, by which, as Harvey observed, the question was so much obacured that physicians were unable to give a correct explanation of the phenomena. However, the consideration of the obvious use of the valves of the pulmonary artery had led Galen to maintain that a portion of the blood contained in that vessel passed through the lungs into the pulmonary veins, but this passage he sup posed to depend more upon the action of the lungs themselves than of the heart. Harvey carried out this argument still further, and maintained from it that the whole of the blood which is propelled from the right side passes through the lungs to the left side of the heart. In like manner he showed that the blood is propelled from the left ventricle into the arteries and so distributed to all parts of the body. He next proceeded to give approximate calculations of the quantity of blood which passes from the veins through the heart in a given time. This he showed to be ao much more thao is required for the nutrition, or can be supplied to the veins by the absorption of alimentary substances, that the surplus must of necessity return through the various tissues of the body to the veins again. He then argued from the construction of the valves of the veins that the course of the blood in them must be from the smaller to the larger divisions, and thus to the heart again. These views he still further confirmed by reference to the now well-known effects of ligatures placed on a limb with different degrees of tightness. If the ligature be so placed as to compress the veins alone, they become swelled and tumid beyond the ligature, and quito empty between it and the heart, whilst the pulsations of the artery remain unaltered. If it be drawn a little tighter the pulsations of the artery cease beyond, but are felt more violent than usual just within the ligature.
Such is a brief abstract of the principal steps in this the greatest and most original discovery in physiology, which was so directly opposed to all tho previous notions of physicians, that its author might well observe, "Adeo nova aunt at inaudita ut non solum ex ineidia quorundam metuam =alum milli, sod verear ne habeam inimicos omnes homines tantnm consuetude ant semel inibibita doctrine altisque defixa mdicibua quasi altera nature., spud omnea valet, et antiquitatis veneranda suspicio cogit." This anticipation proved correct; for Harvey afterwards complained to one of his friends, that his practice fell off considerably after the publication of his treatise On the Circulation of the Blood,' and it is well known that the doctrine was not received by any physician who was more than forty years old. His opinions were violently opposed by Primi rosins, Parisanue, Riolanus (1645), and others. Pasisanus was ably refuted by his friend Dr. George Ent, Fellow of the College of Physicians, and other advocates of Harvey's views appeared on the Continent. The only man who was honoured by a reply from Harvey himself was Riolanus, professor of anatomy in Paris, in answer to whom he published two letters. In 1652 Harvey had the satisfac tion of seeing one of his early opponents, P/ecnpitie, professor at Louvain, declare himself a convert to his opinions, and by his example many more were induced to withdraw their opposition. Iu the whole of this.controversy, says Sprengel (' Hist of Med.,' sect. xii., c. 1), the discretion and rare modesty of Harvey afford the best model for naturalists and scientific writers.
Harvey had been so much disgusted by the disputes in which he was involved on the publication of his views on the circulation of the blood that he had determined to publish nothing more, and it was only at the earnest request of his friend Dr. Ent that he was induced to allow his Exercitationes de Generatione ' to be printed. This work consists partly of a commentary upon the writings of Aristotle and Fabricus ab Aquapendents on the same subject, and partly of details of his own observations and experiments. The earlier 'Exercitationes' contain a description of the organs of generation in the common fowl, of the formation of the egg and its extrusion from the body, and of the use and nature of its various parts, as well as the changes which it undergoes during the process of incubation. He then proceeds to enter
upon some discussions on the nature of the act of generation, and of the degree in which the male and female respectively contribute to its performance, in the course of which he examines the opinions of Aristotle upon this abstruse subject, and advances some of his own. The concluding treatises contain a description of the analogous processes in the deer.
Without venturing upon an abstract of the whole contents of these papers, we shall endeavour to give some idea of the knowledge possessed by Harvey, and especially of his own discoveries and additions to this most interesting branch of physiology. He described the organs of generation in the fowl : he observed that the vitellus or yoke is at first in vascular connection with the parent, that this connection is after wards broken off, and that in its passage through the oviduct the layers of albumen are added, and that before its final extrusion from the body of the mother the hard shell was formed : he asserted that all these parts, even the shell itself, are formed from the same sub stance under the influence of the assimilative power of the egg itself, and are not mere secretions from the organs of the parent, as was previously supposed : he was the first too describe accurately the two layers of albumen, and to show that each is contained in its own proper membrane : he was aware that the shell is porous, and admits of the respiration of the chick through it : be described the chalazee at each end of the egg, and showed that they exist in the unimpregnated as well as the impregnated egg; whereas it had been previously supposed, and especially by his master Fabricius, that these parts represeut the germ from which the future chick was to be formed. The greatest discovery however made by Harvey in this branch of physiology was the use and importance of the ' cicatricula,' which he showed to he the true germ in which all the future changes take place, and for the increate and nutrition of which all the other parts of the egg are destined. He showed that it is present before the yoke has left the ovary, and pointed out the error of Fabricus, who considered it the 'remains of the pedicle by which the vitellus was attached to the ovary: he was aware that eggs occasionally contain a double yolk, and asserted that twine are produced from such eggs, but that they do not survive. The fifteenth and seven following 'Exercitationes' contain a description of the changes which the egg undergoee from the first to the fourteenth day of incubation. He described minutely the changes which take place in the cicatricula at the eud of the second day. These observa tions appear to have been quite original :—" At this time it attains the size of the finger-nail nearly ; two and sometimes three concentric layers may be observed in it. The central one is the most transparent of the two. In the middle of it is s white speck, which from its appearance may be compared to a cataract in the centre of the pupil of the eye. During this day the central layer especially enlarges and entrenches upon the external one." This description appears to accord with that of the ' area pellucida; to which so much importance is attached by later writers on this subject. "At the end of the third day a pulsating spot may be observed in the centre of the oicatricula,' which forms the rudiment of the future heart." He observed that the pulsations may be called forth afresh, when languid or intermitted, by the employment of various stimuli: he showed that the liver is formed round the umbilical vein, but he does not seem to have been aware that the liver, as well as all the other glands whose duets com municate with the intestinal canal, is a prolongation or growth from the intestinal sac : he described five umbilical vessels, of which three are veins and two arteries, one of the veins being distributed to the albumen, the other four vessels to the vitellus. The first-mentioned vela goes to the rens care, the other two to the vena porta, just before it enters the liver. The arteries are branches of the common iliac+. On this point, though his observations are correct as far as they go, his knowledge fell short of that of later inquirers; for he does not appear to have had any very accurate acquaintance with the uses of the allantoia. lie was aware that the vitellus is drawn into the Intestine of the chick shortly before hatching, and serves for its early nutriment ; and in this relation ho well compared it to the milk. This fact wee known to Aristotle. He corrected the error of Fabricius, who suppo.ed that the egg is chipped by the hen, and showed on the contrary that this process is performed by the chick itself.