She was at that time in Holstein; and Swammerdam wrote to a friend of his who accompanied her, to obtain permission to consult her in writing respecting his doubts. The result of their correspondence was a resolution on his part no longer to addict himself exclusively to pursuits which had reference to this world only, but to endeavour to make his peace with God. He did not, however, entirely relinquish his anatomical studies, but on the contrary engaged with astonishing ardour in the examination of the structure of bees, which he finished on the last day of September 1674. "He had laboured so assiduously at this work," says Boerhaave, "as to destroy his constitution; nor did he ever recover even a shadow of his former strength. The labour, in fact, was beyond the power of ordinary men: all day he was occupied in examining subjects, and at night described and delineated what he had seen by day. At six in the morning, in summer, he began to receive sufficient light from the sun to enable him to trace the objects of his examination. He continued dissecting till twelve, with his hat removed lest it should impede the light, and in the full blaze of the sun, the heat of which caused his head to be constantly covered with a profuse perspiration. His eyes being continually employed in this strong light, the effect of which was increased by the use of the microscope, they were so affected by it, that after mid-day he could no longer trace the minute bodies which he examined, although he had then as bright a light as in the forenoon." A month of this excessive labour was necessary to examine and depict the intestines of bees alone; and the investigation of their entire structure cost him much additional labour; and all this was done, with a body debilitated by disease, and a mind agitated by conflicting passions, amid sighs and tears. At one time the bent of his disposition impelled him to investigate the wonderful works of Omnipotence; at another a voice within told him that he ought to set his affections on God alone. After finishing his examination of the structure of bees, he was so affected with remorse, that he gave the manuscript and drawings to a friend, careless what might happen to them. At the same time, however, he wrote two letters to Boccone, on the nature of corals.
These occupations being ended, he was more powerfully impressed than ever with the vanity of human pursuits, and after this period he never engaged in his customary investigations. He acknowledged that hitherto ambition alone had incited him to undergo so many labours, but now resolved to devote the remainder of his life to the cultivation of Christian piety. Being encouraged in this resolution by the approbation of Antoinette Bourignon, he firmly adhered to it; and estimating the annual sum necessary for his subsistence at 400 Dutch florins, he endeavoured to dispose of his collections, which formed the only treasures that he possessed. For this purpose, he applied to Thevenot, who, however, was unable to find a purchaser in France. He then had recourse to another friend, Nicolas Steno, who had abjured the Protestant faith and was living at Florence, and whom he requested to represent the matter to the Grand Duke of Tuscany, in case he might feel disposed to purchase them. This person advised him to follow his example, relinquish his creed, embrace the Catholic faith, and proceed to Florence, promising that he should induce the duke to accept the offer. Swammerdam replied indignantly, that he would not sell his soul for money.
Being without any fixed occupation, he devoted his leisure to arranging and cleaning the contents of his museum, and writing out a catalogue of them. They consisted of anatomical preparations and insects, of the latter of which there were nearly three thousand distinct species. These were all described and arranged into classes, and the entire structure of many of them had been demonstrated by the most minute dissection. He then published his Treatise on the Ephemeris, which he had commenced when in France, and which is considered as one of the most remarkable productions of any age. He did not, however, venture upon this step without consulting Bourignon. These arrangements completed, he now determined in earnest to lead a holy life, and being desirous of a personal consultation with his directress, he went to Holstein, where he remained with her some time. On returning to Amsterdam, he again endeavoured to dispose of his museum, but without success; and his sister, who had hitherto presided over the domestic establishment, happening at this time to be married, his father resolved upon living with his son-in-law, so that he was obliged to look out for another residence. On this occasion his allowance was limited to 200 florins, and as he could not find any one to purchase his collection he was reduced to great perplexity. However, a thought struck him that he might apply to an old friend, who had formerly treated him with great kindness; but in this he also failed.
In the following year, his father died, leaving him heir to his property, which was sufficient for his support; but he became involved in disputes with his sister, which, together with his assiduous endeavours to discharge his religious duties, so agitated his mind, that he was again seized with a severe ague. For three entire months he was confined to his bed, and even when the accessions of the fever had become more gentle and less frequent, he still persisted in remaining in the house. In vain did his friends, Sladus, Ruysch, Schrader, Hotton, and Guenellon, urge upon him the propriety of adopting means for improving his health. He would not yield to their proposals; and, when they still persisted, at length maintained an obstinate silence.
Finding all his endeavours to sell his collection fruitless, he determined to expose it to public auction; but before the period arrived, his disease was much aggravated by the various agitations to which his mind was now habitually subject. The fever proved again regular and continuous, the countenance was emaciated, the eyes were sunk, the feet, the legs, and at length the whole body, dropsical. His friends dared not speak to him respecting his former studies, for he detested all allusion to them, and wished to withdraw his mind entirely from earthly concerns. At length, on the 25th January 1670, when he perceived his end approaching, he wrote his will, leaving to Thevenot all his original manuscripts on the history of bees, butterflies, and anatomy, with 52 plates; all of which were at that time in the house of Herman Wigendorp in Leyden, to whom they had been delivered to be translated into Latin. He bequeathed his property to Margaret Volckers, wife of Daniel de Hoest, appointing her and Christopher Wyland his executors. The remainder of his time he spent in devotion, and died on the 17th February.
It was some years before Thevenot obtained possession of the manuscripts, and after his death they passed into various hands, but were bought in 1727 by the illustrious Boerhaave, who arranged and published them in two folio volumes, prefixing a life of the author, from which we have drawn the materials of this notice.
The learned editor gives an interesting account of the instruments and expedients employed by Swammerdam in dissecting insects and other minute animals. When the anatomical preparations, insects, and apparatus, were offered for sale, no purchaser could be found, and the collection was subsequently dispersed. The manuscripts and drawings of the Biblia Naturæ were deposited by Boerhaave in the library of the University of Leyden.
The works of Swammerdam contain more original and accurate observations than those of any naturalist who preceded him, excepting Aristotle. He refuted numerous errors committed by his predecessors, and carried his observations to a degree of minuteness and accuracy truly astonishing; but it is not a little surprising that he succeeded less in describing the structure of large objects than in delineating the organs of the most minute.
His classification of insects differs very materially from those now in use. The characters of his four classes he derives from the state in which each insect appears after its birth, and those through which it passes before attaining its entire development. In the first he places all those which issue from the egg with nearly the same form as that which they have at the period of their full growth; such as spiders, slugs, leeches, &c. In the second are included those which, like the grashopper, issue with six feet, and some time after cast off the covering under which the wings were concealed. These insects run or leap with agility in their first stage, which is not the case with those of the next class. To the third are referred insects which undergo greater changes, such as caterpillars, and which proceed from the egg in the state of a worm, remain in that state for some time, cast off their hairy covering, assume the form of a chrysalis, when they become motionless, and finally emerge in a winged state. The fourth class consists of such as, like the common fly, on changing the form under which they issued from the egg to assume that of a worm, do not cast their covering, but become separated from it, while it remains and forms a shell or egg-like investiture, in which the insect remains in the pupa state until it finally emerges with wings.
The history of Swammerdam must excite our sympathy and commiseration; but that, as some have alleged, he lost his reason towards the end of his life, and became subject to mania, arising from religious melancholy, no one who has any share of that piety which he evinced will feel disposed to admit. Although he lived in misery, the close of his life was perhaps more enviable than that of many who have gone smiling to their final rest; and it is well for those who, before the period arrives when as the tree falls so it must lie, can like him become truly sensible of the vanity of all earthly pursuits, even although after death they should be pointed out as the victims of a distempered imagination.