His theory of medicine is amusing, if not instructive. He supposes the human body to consist of a cerebroso-medullary part, of which the nerves are processes; and a cortical part, including the vascular system and its fluids. The nervous system, which is the animated part, derives its nourishment from the finer fluids of the vascular system, and its energy from an electrical principle inhaled by the lungs. The circulating fluids are capable of being vitiated by acescent or putrid ferments, the former acting on the serum, and causing critical fevers; the latter on the crassamentum, and exciting phlogistic diseases. Eruptive ailments are excited by external causes, which he supposes to be animalcula. The cortical or vascular system undergoing continual waste, requires continual reparation, which is effected by means of suitable diet. Its diseases arise from improper food, and are to be remedied by sapid medicines; while those of the medullary system are cured by olid substances.
Systems of nosology, theories of medicine, and classifications of natural objects and phenomena, agree in this one respect, that they are all eagerly embraced, strenuously defended, fall into disuse, and become subjects of ridicule. Such must be the fate of the Linnæan system of botany, as it has been of the other fancies of its author; and such must be the fate of every system not founded on organic structure and its modifications, or upon external form as connected with internal disposition.
In 1766, he published a small work extending to only twenty-nine pages, entitled Clavis Medicinæ duplex, Exterior et Interior, which may be considered as a syllabus of his lectures. It contains a view of his theory of medicine, and an arrangement of drugs in thirty orders, according to their sensible qualities.
The last book which he produced was a continuation of his Mantissa, containing new species and genera, with a variety of emendations. Such of his writings as have not been already mentioned, will be noticed in a subsequent section; and in the mean time we resume our narrative, remarking, that few individuals had a longer scientific career than he; forty-four years having elapsed between the appearance of his first tract, the Hortus Uplandicus (in 1731) and the Mantissa (in 1771).
It would appear that Linnæus possessed a good constitution, although we have seen him suffering under attacks of rheumatism, nephritis, and gout. In 1764, as already mentioned, he had a violent attack of pleurisy; after which he passed the period of his convalescence at his villa of Hammarby, where, on the 9th July, he celebrated the 25th anniversary of his marriage. The same year he had the pleasure of marrying his eldest daughter to Lieutenant Bergencrantz.
It does not seem very easy to determine the precise nature of the disease under which he laboured, although it is probable that it was rheumatism and not gout. In the Latin diary of Dr Gieseke, as quoted by Stoever, is the following passage relative to this subject:—"In 1750, I (Linnæus) had such a violent attack of rheumatism (malum ischiadicum), that I had great difficulty in getting home. For a whole week the pain, which was insupportable, prevented me from sleeping; for which reason I would have taken opium, but was prevented by a friend who came in on the seventh evening. My wife asked me if I would eat some strawberries. I will try, said I. It was about the beginning of the strawberry-season, and they were in good condition. Half an hour after, I fell asleep, and continued so till two in the morning. When I awoke, I wondered that the pain had abated, and asked whether I had been asleep, which the persons who were watching assured me had been the case. I asked if they had more of the strawberries, and ate up the remainder. I then slept till daylight, when the pain was about my ankles. Next day I ate as many strawberries as I could, and on the second morning was free of pain. I thought that mortification had taken place; but the part was entire, and I was able to get up, although I felt weak. Next year, about the same time, I had an attack, and another the following year, but milder, and it was always alleviated by the strawberries; and from that time I have been free of the disease." This conversation took place in 1771.
In the spring of 1772, he was visited by Dr Murray, professor of medicine and botany at Gottingen, who had been one of his pupils, and had long enjoyed his confidence and esteem. At this period he possessed good health, and was as ardent as ever in his endeavours for the improvement of science. He was appointed rector of the university for the third time, and, during the six months in which he discharged the duties of that office, the conduct of the young men was highly exemplary. When he retired, deputations from all the nations of the students came to present their warmest thanks, and to beg his permission to print the address which he delivered on resigning.
In 1773, he had another attack of lumbago, and was moreover affected with an epidemic sore throat; but on the whole his health did not suffer materially. This year, a committee of six bishops, six doctors of divinity, and eight literary and scientific individuals, was appointed by the government to undertake a better translation of the Bible into the Swedish language. Linnæus was among the number, having been chosen on account of his knowledge of the animals and plants mentioned in the Scriptures; but it does not appear that he ever engaged seriously in the undertaking, although he made two journeys to Stockholm for the purpose.
While delivering one of his lectures in the botanic garden, in the beginning of May 1774, he had a slight attack of apoplexy, from which he did not recover for some time; and from this period his health rapidly declined. It is said, that the vexation produced by the publication of a letter in which he had confidentially disclosed to a friend the history of his youth, and especially the progress of his courtship, was the exciting cause of this fatal affection. The illustrious Haller, with whom he had corresponded from 1737 to 1766, published a volume of letters, written in Latin by men of literary eminence, and addressed to himself; and, having been always extremely jealous of Linnæus, thought proper to print all his epistles, in order to defend his own character against the accusations of envy which had been but too justly preferred. When he read these communications he was violently agitated, and from that moment his health became perceptibly worse. The apoplectic attack followed soon after; and from a comparison of testimonies on the subject, it seems to us extremely probable that it was occasioned by the causes now assigned.
He did not, however, despair, nor give himself up to inactivity under these distressing circumstances. A Swedish gentleman returning from Surinam, where he had been residing on his estates, brought with him a collection of plants preserved in spirits of wine, which he presented to the king. The latter sent them to Linnæus, whose health was much benefited by the pleasure which the possession of these treasures inspired. He immediately commenced a description of them, which was published in the Amænitates Academicæ,—a work respecting which we shall have occasion to speak in another section.