Harvey’s Work on Generation.—We have seen how Dr. Ent persuaded his friend to publish this book in 1651. It is between five and six times as long as the Exerc. de motu cord. et sang., and is followed by excursus De partu, De uteri membranis, De conceptione; but, though the fruit of as patient and extensive observations, its value is far inferior. The subject was far more abstruse, and in fact inaccessible to proper investigation without the aid of the microscope. And the field was almost untrodden since the days of Aristotle. Fabricius, Harvey’s master, in his work De formatione ovi et pulli (1621), had alone preceded him in modern times. Moreover, the seventy-two chapters which form the book lack the co-ordination so conspicuous in the earlier treatise, and some of them seem almost like detached chapters of a system which was never completed or finally revised.
Aristotle had believed that the male parent furnished the body of the future embryo, while the female only nourished and formed the seed; this is in fact the theory on which, in the Eumenides of Aeschylus, Apollo obtains the acquittal of Orestes. Galen taught almost as erroneously that each parent contributes seeds, the union of which produced the young animal. Harvey, after speaking with due honour of Aristotle and Fabricius, begins rightly “ab ovo”; for, as he remarks, “eggs cost little and are always and everywhere to be had,” and moreover “almost all animals, even those which bring forth their young alive, and man himself, are produced from eggs” (“omnia omnino animalia, etiam vivipara, atque hominem adeo ipsum, ex ovo progigni”). This dictum, usually quoted as “omne vivurn ex ovo,” would alone stamp this work as worthy of the discoverer of the circulation of the blood, but it was a prevision of genius, and was not proved to be a fact until K. E. von Baer discovered the mammalian ovum in 1827. Harvey proceeds with a careful anatomical description of the ovary and oviduct of the hen, describes the new-laid egg, and then gives an account of the appearance seen on the successive days of incubation, from the 1st to the 6th, the 10th and the 14th, and lastly describes the process of hatching. He then comments upon and corrects the opinions of Aristotle and Fabricius, declares against spontaneous generation (though in one passage he seems to admit the current doctrine of production of worms by putrefaction as an exception), proves that there is no semen foemineum, that the chalazae of the hen’s eggs are not the semen galli, and that both parents contribute to the formation of the egg. He describes accurately the first appearance of the ovarian ova as mere specks, their assumption of yelk and afterwards of albumen. In chapter xlv. he describes two methods of production of the embryo from the ovum: one is metamorphosis, or the direct transformation of pre-existing material, as a worm from an egg, or a butterfly from an aurelia (chrysalis); the other is epigenesis, or development with addition of parts, the true generation observed in all higher animals. Chapters xlvi.-l. are devoted to the abstruse question of the efficient cause of generation, which, after much discussion of the opinions of Aristotle and of Sennertius, Harvey refers to the action of both parents as the efficient instruments of the first great cause.[1] He then goes on to describe the order in which the several parts appear in the chick. He states that the punctum saliens or foetal heart is the first organ to be seen, and explains that the nutrition of the chick is not only effected by yelk conveyed directly into the midgut, as Aristotle taught, but also by absorption from yelk and white by the umbilical (omphalomeseraic) veins; on the fourth day of incubation appear two masses (which he oddly names vermiculus), one of which develops into three vesicles, to form the cerebrum, cerebellum and eyes, the other into the breastbone and thorax; on the sixth or seventh day come the viscera, and lastly, the feathers and other external parts. Harvey points out how nearly this order of development in the chick agrees with what he had observed in mammalian and particularly in human embryos. He notes the bifid apex of the foetal heart in man and the equal thickness of the ventricles, the soft cartilages which represent the future bones, the large amount of liquor amnii and absence of placenta which characterize the foetus in the third month; in the fourth the position of the testes in the abdomen, and the uterus with its Fallopian tubes resembling the uterus bicornis of the sheep; the large thymus; the caecum, small as in the adult, not forming a second stomach as in the pig, the horse and the hare; the lobulated kidneys, like those of the seal (“vitulo,” sc. marino) and porpoise, and the large suprarenal veins, not much smaller than those of the kidneys (li.-lvi). He failed, however, to trace the connexion of the urachus with the bladder. In the following chapters (lxiii.-lxxii.) he describes the process of generation in the fallow deer or the roe. After again insisting that all animals arise from ova, that a “conception” is an internal egg and an egg an extruded conception, he goes on to describe the uterus of the doe, the process of impregnation, and the subsequent development of the foetus and its membranes, the punctum saliens, the cotyledons of the placenta, and the “uterine milk,” to which Sir William Turner recalled attention in later years. The treatise concludes with detached notes on the placenta, parturition and allied subjects.
Harvey’s other Writings and Medical Practice.—The remaining writings of Harvey which are extant are unimportant. A complete list of them will be found below, together with the titles of those which we know to be lost. Of these the most important were probably that on respiration, and the records of post-mortem examinations. From the following passage (De partu, p. 550) it seems that he had a notion of respiration being connected rather with the production of animal heat than, as then generally supposed, with the cooling of the blood. “Haec qui diligenter perpenderit, naturamque aeris diligenter introspexerit, facile opinor fatebitur eundem nec refrigerationis gratia nec in pabulum animalibus concedi. Haec autem obiter duntaxat de respiratione diximus, proprio loco de eadem forsitan copiosius disceptaturi.”
Of Harvey as a practising physician we know very little. Aubrey tells us that “he paid his visits on horseback with a foot-cloth, his man following on foot, as the fashion then was.” He adds—“Though all of his profession would allow him to be an excellent anatomist, I never heard any that admired his therapeutic way. I knew several practitioners that would not have given threepence for one of his bills” (the apothecaries used to collect physicians’ prescriptions and sell or publish them to their own profit), “and that a man could hardly tell by his bill what he did aim at.” However this may have been,—and rational therapeutics was impossible when the foundation stone of physiology had only just been laid,—we know that Harvey was an active practitioner, performing such important surgical operations as the removal of a breast, and he turned his obstetric experience to account in his book on generation. Some good practical precepts as to the conduct of labour are quoted by Percivall Willughby (1596–1685). He also took notes of the anatomy of disease; these unfortunately perished with his other manuscripts. Otherwise we might regard him as a forerunner of G. B. Morgagni; for Harvey saw that pathology is but a branch of physiology, and like it must depend first on accurate anatomy. He speaks strongly to this purpose in his first epistle to Riolan: “Sicut enim sanorum et boni habitus corporum dissectio plurimum ad philosophiam et rectam physiologiam facit, ita corporum morbosorum et cachecticorum inspectio potissimum ad pathologiam philosophicam.” The only specimen we have of his observations in morbid anatomy is his account of the post-mortem examination made by order of the king on the body of the famous Thomas Parr, who died in 1635, at the reputed age of 152. Harvey insists on the value of physiological truths for their own sake, independently of their immediate utility; but he himself gives us an interesting example of the practical application of his theory of the circulation in the cure of a large tumour by tying the arteries which supplied it with blood (De generat. Exerc. xix.).
The following is believed to be a complete list of all the known writings of Harvey, published and unpublished:—
Exercitatio anatomica de motu cordis et sanguinis, 4to (Frankfort-on-the-Main, 1628); Exercitationes duae anatomicae de circulatione sanguinis, ad Johannem Riolanum, filium, Parisiensem (Cambridge, 1649); Exercitationes de generatione animalium, quibus accedunt quaedam de partu, de membranis ac humoribus uteri, et de conceptione, 4to (London, 1651); Anatomia Thomae Parr, first published in the treatise of Dr John Betts, De ortu et natura sanguinis, 8vo (London, 1669). Letters: (1) to Caspar Hoffmann of Nuremberg, May 1636; (2) to Schlegel of Hamburg, April 1651; (3) three to Giovanni Nardi of Florence, July 1651, Dec. 1653 and Nov. 1655; (4) two to Dr Morison of Paris, May 1652; (5) two to Dr Horst of
- ↑ So in Exerc. liv.: “Superior itaque et divinior opifex, quam est homo, videtur hominem fabricare et conservare, et nobilior artifex, quam gallus, pullum ex ovo producere. Nempe agnoscimus Deum, creatorem summum atque omnipotentem, in cunctorum animalium fabrica ubique praesentem esse, et in operibus suis quasi digito monstrari: cujus in procreatione pulli instrumenta sint gallus et gallina.... Nec cuiquam sane haec attributa conveniunt nisi omnipotenti rerum Principio, quocunque demum nomine idipsum appellare libuerit: sive Mentem divinam cum Aristotele, sive cum Platone Animam Mundi, aut cum aliis Naturam naturantem, vel cum ethnicis Saturnum aut Iovem; vel potius (ut nos decet) Creatorem ac Patrem omnium quae in coelis et terris, a quo animalia eorumque origines dependent, cujusque nutu sive effatu fiunt et generantur omnia.”
