An attack of inflammation of the lungs in the spring of 1759 having produced symptoms threatening consumption, by which the promising medical career of his brother James had been cut short, Hunter obtained in October 1760 the appointment of staff-surgeon in Hodgson and Keppel’s expedition to Belleisle. With this he sailed in 1761. In the following year he served with the English forces on the frontier of Portugal. Whilst with the army he acquired the extensive knowledge of gunshot wounds embodied in his important treatise (1794) on that subject, in which, amongst other matters of moment, he insists on the rejection of the indiscriminate practice of dilating with the knife followed almost universally by surgeons of his time. When not engaged in the active duties of his profession, he occupied himself with physiological and other scientific researches. Thus, in 1761, off Belleisle, the conditions of the coagulation of the blood were among the subjects of his inquiries.[6] Later, on land, he continued the study of human anatomy, and arranged his notes and memoranda on inflammation; he also ascertained by experiment that digestion does not take place in snakes and lizards during hibernation, and observed that enforced vigorous movement at that season proves fatal to such animals, the waste so occasioned not being compensated, whence he drew the inference that, in the diminution of the power of a part attendant on mortification, resort to stimulants which increase action without giving real strength is inadvisable.[7] A MS. catalogue by Hunter, probably written soon after his return from Portugal, shows that he had already made a collection of about two hundred specimens of natural and morbid structures.
On arriving in England early in 1763, Hunter, having retired from the army on half-pay, took a house in Golden Square, and began the career of a London surgeon. Most of the metropolitan practice at the time was held by P. Pott, C. Hawkins, Samuel Sharp, Joseph Warner and Robert Adair; and Hunter sought to eke out his at first slender income by teaching practical anatomy and operative surgery to a private class. His leisure was devoted to the study of comparative anatomy, to procure subjects for which he obtained the refusal of animals dying in the Tower menagerie and in various travelling zoological collections. In connexion with his rupture of a tendo Achillis,[8] in 1767, he performed on dogs several experiments which, with the illustrations in his museum of the reunion of such structures after division, laid the foundation of the modern practice of cutting through tendons (tenotomy) for the relief of distorted and contracted joints. In the same year he was elected F.R.S. His first contribution to the Philosophical Transactions, with the exception of a supplement to a paper by J. Ellis in the volume for 1766, was an essay on post-mortem digestion of the stomach, written at the request of Sir J. Pringle, and read on the 18th of June 1772, in which he explained that phenomenon as a result of the action of the gastric juice.[9] On the 9th of December 1768 he was elected a surgeon to St George’s Hospital, and, soon after, a member of the Corporation of Surgeons. He now began to take house-pupils. Among these were Edward Jenner, who came to him in 1770, and until the time of Hunter’s death corresponded with him on the most intimate and affectionate terms, W. Guy, Dr P. S. Physick of Philadelphia, and Everard Home, his brother-in-law. William Lynn and Sir A. Carlisle, though not inmates of his house, were frequent visitors there. His pupils at St George’s included John Abernethy, Henry Cline, James Earle and Astley Cooper. In 1770 he settled in Jermyn Street, in the house which his brother William had previously occupied; and in July 1771 he married Anne, the eldest daughter of Robert Home, surgeon to Burgoyne’s regiment of light horse.[10]
From 1772 till his death Hunter resided during autumn at a house built by him at Earl’s Court, Brompton, where most of his biological researches were carried on. There he kept for the purpose of study and experiment the fishes, lizards, blackbirds, hedgehogs and other animals sent him from time to time by Jenner; tame pheasants and partridges, at least one eagle, toads, silkworms, and many more creatures, obtained from every quarter of the globe. Bees he had under observation in his conservatory for upwards of twenty years; hornets and wasps were also diligently studied by him. On two occasions his life was in risk from his pets—once in wrestling with a young bull, and again when he fearlessly took back to their dens two leopards which had broken loose among his dogs.
Choosing intuitively the only true method of philosophical discovery, Hunter, ever cautious of confounding fact and hypothesis, besought of nature the truth through the medium of manifold experiments and observations. “He had never read Bacon,” says G. G. Babington, “but his mode of studying nature was as strictly Baconian as if he had.”[11] To Jenner, who had offered a conjectural explanation of a phenomenon, he writes, on the 2nd of August 1775: “I think your solution is just; but why think? why not try the experiment? Repeat all the experiments upon a hedgehog[12] as soon as you receive this, and they will give you the solution.” It was his axiom however, “that experiments should not be often repeated which tend merely to establish a principle already known and admitted, but that the next step should be the application of that principle to useful purposes” (“Anim. Oecon.,” Works, iv. 86). During fifteen years he kept a flock of geese simply in order to acquaint himself with the development of birds in eggs, with reference to which he remarked: “It would almost appear that this mode of propagation was intended for investigation.” In his toxicological and other researches, in which his experience had led him to believe that the effects of noxious drugs are nearly similar in the brute creation and in man, he had already, in 1780, as he states, “poisoned some thousands of animals.”[13]
By inserting shot at definite distances in the leg-bones of young pigs, and also by feeding them with madder, by which all fresh osseous deposits are tinged,[14] Hunter obtained evidence that bones increase in size, not by the intercalation of new amongst old particles, as had been imagined by H. L. Duhamel du Monceau, but by means of additions to their extremities and circumference, excess of calcareous tissue being removed by the absorbents. Some of his most extraordinary experiments were to illustrate the relation of the strength of constitution to sex. He exchanged the spurs of a young cock and a young pullet, and found that on the former the transplanted structure grew to a fair size, on the latter but little; whereas a spur from one leg of a cock transferred to its comb, a part well supplied with blood, grew more than twice as fast as that left on the other leg. Another experiment of his, which required many trials for success, was the engrafting of a human incisor on the comb of a cock.[15] The uniting of parts of different animals when brought into contact he attributed to the production of adhesive instead of suppurative inflammation, owing to their possession of “the simple living principle.”[16] The effects of habit upon structure were illustrated by Hunter’s observation that in a sea-gull which he had brought to feed on barley the muscular parietes of the gizzard became greatly thickened. A similar phenomenon was noticed by him in the case of other carnivorous birds fed on a vegetable diet.
It was in 1772 that Hunter, in order effectually to gauge the extent of his own knowledge, and also correctly to express his views, which had been repeatedly misstated or ascribed to others, began his lectures on the theory and practice of surgery, at first delivered free to his pupils and a few friends, but subsequent to 1774 on the usual terms, four guineas. Though Pott, indeed, had perceived that the only true system of surgery is that which most closely accords with the curative efforts of nature, a rational pathology can hardly be said to have had at this time any existence; and it was generally assumed that a knowledge of anatomy alone was a sufficient foundation for the study of surgery. Hunter, unlike his contemporaries, to most of whom his philosophic habit of thought was a mystery, and whose books contained little else than relations of cases and modes of treatment, sought the reason for each phenomenon that came under his notice. The principles of surgery, he maintained, are not less necessary to be understood than the principles of other sciences; unless, indeed, the surgeon should wish to resemble “the Chinese philosopher whose knowledge consisted only in facts.” Too much attention, he remarked, cannot be paid to facts; yet a multitude of facts overcrowd the memory without advantage if they do not lead us to establish principles, by an acquaintance with which we learn the causes of diseases. Hunter’s course, which latterly comprised eighty-six lectures, delivered on alternate evenings between the hours of seven and eight, lasted from October to April. Some teachers of his time were content to dismiss the subjects of anatomy and surgery in a course of only six weeks’ duration. His class was usually small and never exceeded thirty. He was deficient in the gifts of a good extempore speaker, being in this respect a remarkable contrast to his brother William; and he read his lectures, seldom raising his eyes from the manuscript. His manner with his auditory is stated to have been embarrassed and awkward, or, as Adams puts it (Obs. on Morbid Pois., p. 272), “frequently ungraceful,” and his language always unadorned; but that his “expressions for the explaining of his new theories rendered his lectures often unintelligible” is scarcely evident in his pupils’ notes still extant. His own and others’ errors and fallacies were exposed with equal freedom in his teaching. Occasionally he would tell his pupils, “You had better not write down that observation, for very likely I shall think differently next year”; and once in answer to a question he replied, “Never ask me what I have said or what I have written; but, if you will ask me what my present opinions are, I will tell you.”
In January 1776 Hunter was appointed surgeon-extraordinary to the king. He began in the same year his Croonian lectures on muscular motion, continued annually, except in 1777, till 1782: they were never published by him, being in his opinion too incomplete. In 1778 appeared the second part of his Treatise on the Natural History of the Human Teeth, the first part of which was published in 1771. It was in the waste of the dental alveoli and of the fangs of shedding teeth that in 1754-1755, as he tells us, he received his first hint of the use of the absorbents. Abernethy (Physiological Lectures, p. 196) relates that Hunter, being once asked how he could suppose it possible for absorbents to do such things as he attributed to them, replied, “Nay, I know not, unless they possess powers similar to those which a caterpillar exerts when feeding on a leaf.” Hunter in 1780 read before the Royal Society a paper in which he laid claim to have been the first to make out the nature of the utero-placental circulation. His brother William, who had five years previously described the same in his Anatomy of the Gravid Uterus, thereupon wrote to the Society attributing to himself this honour. John Hunter in a rejoinder to his brother’s letter, dated the 17th of February 1780, reiterated his former statement, viz. that his discovery, on the evening of the day in 1754 that he had made it in a specimen injected by a Dr Mackenzie, had been communicated by him to Dr Hunter. Thus arose an estrangement between the two Hunters, which continued until the time of William’s last illness, when his brother obtained permission to visit him.
In 1783 Hunter was elected a member of the Royal Society of Medicine and of the Royal Academy of Surgery at Paris, and took part in the formation of “A Society for the Improvement of Medical and Chirurgical Knowledge.”[17] It appears from a letter by Hunter that in the latter part of 1783, he, with Jenner, had the subject of colour-blindness under consideration. As in that year the lease of his premises in Jermyn Street was to expire, he purchased the twenty-four years’ leasehold of two houses, the one on the east side of Leicester Square, the other in Castle Street with intervening ground. Between the houses he built in 1783-1785, at an expense of above £3000, a museum for his anatomical and other collections which by 1782 had cost him £10,000. The new edifice consisted of a hall 52 ft. long by 28 ft. wide, and lighted from the top, with a gallery all round, and having beneath it a lecture theatre. In April 1785 Hunter’s collections were removed into it under the superintendence of Home and William Bell,[18] and another assistant, André. Among the foreigners of distinction who inspected the museum, which was now shown by Hunter twice a year—in October to medical men, and in May to other visitors—were J. F. Blumenbach, P. Camper and A. Scarpa. In the acquisition of subjects for his varied biological investigations and of specimens for his museum, expense was a matter of small moment with Hunter. Thus he endeavoured, at his own cost, to obtain information respecting the Cetacea by sending out a surgeon to the North in a Greenland whaler. He is said, moreover, to have given, in June 1783, £500 for the body of O’Brien, or Byrne, the Irish giant, whose skeleton, 7 ft. 7 in. high, is so conspicuous an object in the museum of the College of Surgeons of London.[19]
Hunter, who in the spring of 1769-1772 had suffered from gout, in spring 1773 from spasm apparently in the pyloric region, accompanied by failure of the heart’s action (Ottley, Life, p. 44), and in 1777 from vertigo with symptoms of angina pectoris, had in 1783 another attack of the last mentioned complaint, to which he was henceforward subject when under anxiety or excitement of mind.
In May 1785,[20] chiefly to oblige William Sharp the engraver, Hunter consented to have his portrait taken by Sir Joshua Reynolds. He proved a bad sitter, and Reynolds made little satisfactory progress, till one day Hunter, while resting his somewhat upraised head on his left hand, fell into a profound reverie—one of those waking dreams, seemingly, which in his lectures he has so well described, when “the body loses the consciousness of its own existence.”[21] The painter had now before him the man he would fain depict, and, turning his canvas upside down, he sketched out the admirable portrait which, afterwards skilfully restored by H. Farrar, is in the possession of the Royal College of Surgeons. A copy by Jackson, acquired from Lady Bell, is to be seen at the National Portrait Gallery, and St Mary’s Hall, Oxford, also possesses a copy. Sharp’s engraving of the original, published in 1788, is one of the finest of his productions. The volumes seen in Reynolds’ picture are a portion of the unpublished records of anatomical researches left by Hunter at his death, which, with other manuscripts, Sir Everard Home in 1812 removed from his museum, and eventually, in order, it has been supposed, to keep secret the source of many of his papers in the Philosophical Transactions, and of facts mentioned in his lectures, committed to the flames.[22]