Göran Wettrell
Lund, Sweden

Carl Linnaeus as pediatrician

Carl Linnaeus is best known as a botanist through his classification of the sexual system of plants and taxonomy. His interest in botany was noticed from a young age at Växjö Gymnasium by his teacher, provincial physician Johan Rothman, who instructed the young student in botany and medicine. During his later school years, Linnaeus realized that he would educate himself to become both a “botanicus and medicus.”¹

Linnaeus enrolled at Lund University in August 1727 and was offered lodging in the house of Dr. Kilian Stobaeus. He worked diligently, spending much time on botanical studies and excursions in Scania in the spring of 1728. He was also allowed to accompany Doctor Stobaeus on medical visits.^2,3

During a visit to his childhood home in Stenbrohult in the summer of 1728, his former teacher, Doctor Rothman, advised him to move to Uppsala. He enrolled at Uppsala University in September 1728, where medical lectures were few, the botanical garden was neglected, and his finances were meager. However, his botanical knowledge impressed influential professors. He was offered lodging and became a tutor to the children of Professor Olof Rudbeck the younger. In the spring of 1730, he took over demonstrations and lectures in the botanical garden in Uppsala.^1,3,4

Linnaeus also gave public and private lectures on dietetics, the science of lifestyle and health, based on observations from his 1732 journey to Lapland in northern Sweden and ongoing medical studies (Figure 1). In April 1733, he began the manuscript Diaeta naturalis (The Natural Way of Living). Around the same time, he also wrote his dissertation on intermittent fevers, which he presented at the University of Harderwijk, Holland in 1735.

Health advice with a pediatric focus

The manuscript Diaeta naturalis began with fifty health rules (regulae), which were later expanded.⁵ These were based on Hippocratic and Salernitan health principles, structured around six key conditions: fresh air, physical activity, sleep, food, bodily excretion, and mental balance.

Some rules concerned childcare:

• The child shall retain its natural form.
• The infant shall for some years be nourished with mother’s milk.
• Food must not be forced upon the child.
• A child must never be deprived of peace and sufficient sleep.
• The youth years lay the foundation for a good old age.

Linnaeus warned against swaddling infants too tightly, which was thought to damage the brain and cause epilepsy. He stated: “The larger the brain, the greater the intelligence.” One of the most important rules contained advice on infant feeding. He strongly promoted breastfeeding and argued that wet nurses should be carefully selected and examined by a physician. Linnaeus believed that the child should not receive milk at fixed times, but “continually as needed.” He cited examples of substances (laxatives, absinthe) that passed from mother to child through breastmilk. He discouraged in infant feeding the use of cow’s milk compared to wet nursing. The advice on breast feeding was later, in 1752, developed in a separate dissertation entitled “The wet-nurse as stepmother.”⁶

Academic career and medical writing

After three years abroad doing botanical work and scientific authorship in Holland, France, and England, Linnaeus returned to Stockholm and supported himself as a naval and private physician. In 1741 he was appointed professor in practical medicine in Uppsala and soon exchanged subject areas with the other faculty professor, Nils Rosén. Linnaeus was then responsible for botany, materia medica (pharmacology), semiotics (symptomatology), natural history, and dietetics, as well as the management of the botanical garden.³

Linnaeus published two systemic works in medicine. The first was Genera morborum (The Genera of Diseases, 1763), a schematic classification of diseases inspired by his colleague and professor, Francois Boisser de Sauvages, in Montpellier, France.

The second publication was entitled Clavus medicinae duplex (The Two Keys to Medicine, 1766), a short summary of his medical opinions with often difficult-to-understand statements.^7,8 This concise book, according to Linnaeus himself, required “a man’s lifetime before it is understood by the most learned.”⁴

Linnaeus’ knowledge about medicinal plants was presented in his book Materia Medica (1749), considered one of the more important books of the eighteenth century (Figure 2). It contained a careful description of more than 500 plant preparations for the treatment of a hundred or so contemporary medical diseases. His guiding principle was to simplify the arsenal of treatments. He believed that “he who prescribes medicines in long formulas sins either from fraud or from ignorance.”

Linnaeus never published any major work on dietetics. In his old handwritten notes, he expressed his self-esteem by the following statement: “Dietetics has never been treated in a more polite and solid way than by Linnaeus, although he published nothing about it.”¹ However, between 1742 and 1772, he held in Uppsala regular university courses in dietetics, and his views attracted attention. From these lectures, often attended by hundreds of students, there remain several handwritten notes. These and a couple of original manuscripts on dietetics were later found in the Linnean Society’s collections in London.

Linnaeus’ collected advice on health and lifestyle

The first manuscript on health by the young Linnaeus was the previously mentioned Diaeta naturalis. The second consisted of a collection of loose sheets entitled Lachesis naturalis published by the Medical Faculty of Uppsala in 1907.⁹ The manuscript was started as early as 1742–1743. Over the years, notes were added in both Swedish and Latin. Lachesis, a classical goddess of fate, conveyed the natural rules of life. Linnaeus emphasized a simple way of life, moderation, and good habits, where nature was the best physician.³ About health, he stated: “All that we possess in the world are trifling without health. You value others’ happiness in splendor, power and riches. If you have health, you possess what is far greater.”⁹ He divided, in accordance with Hippocrates, early life into seven-year stages (infantia/lactescentia, pueritia, and adolescentia) and pointed to the importance of a good childhood for a healthy lifespan: “Youth gives old age its strength.”¹⁰ He opposed corporal punishment in education: “If one begins to force and beat a boy to the book, he will never learn.” He also stressed the importance of play, moderate work, daily physical activity, and adequate sleep, and he cautioned against excesses during puberty. The importance of heredity was summarized and the optimal situation for a young individual was as follows: “Happy is he who is born of healthy parents in the strongest heat.”

Dissertations and pediatric contributions

Out of Linnaeus’ 180 dissertations, about eighty concerned medical subjects. Several addressed hygiene and child health. In two dissertations, Exanthema viva (1757) and Mundus invisibilis (1767), Linnaeus presented ideas that contagious diseases were caused by a living infectious agent, “animacula viva,” with a specific agent for each disease. This idea, the early germ theory of disease, turned out to be correct more than 100 years later, even if Linnaeus was not alone in such thoughts in the mid-eighteenth century. He believed that living tiny animals, “contagium vivum,” were the cause of whooping cough, smallpox, measles, plague, and leprosy, and that the routes of infection were lungs, throat, stomach, and skin.^3,6,11,12,13 His knowledge about scabies may have been of importance, as he had observed the mites in the skin. He wrote in Mundus invisibilis: “The very smallest animals perhaps cause greater ravages than the largest; indeed, they may take the lives of more than all wars.”¹⁰

Linnaeus showed in letters to his friends a great interest in diseases and health of children. He described in detail serious symptoms and the treatment of his three-year-old daughter, who suffered from remittent fever. His youngest daughter was revived after a difficult birth by the mouth-to-mouth method, insufflatoria medicina.^1,10 As a medical student, he treated his younger sister who had contracted smallpox. The violent, successful cure involved slaughtering a sheep and placing the girl for a few hours inside the warm animal body. On the other hand, Linnaeus recommended that drastic treatments such as bloodletting and purging should only be applied in emergencies.^1,10

Linnaeus’ sharp observations, practical health advice, and simple formulations made him an influential educator. His principles of natural living, moderation, and good habits had an impact on Swedish public and child health.

References

1. Malmeström. E och Uggla,A H. Vita Caroli Linnaei. Carl von Linnés självbiografier. Almquist och Wicksell. Uppsala, 1957.
2. Strandell, B. Linné i Lund. Sydsvenska Medicinhistoriska Sällskapets Årsskrift, 1966.
3. Broberg, G. Mannen som ordnade naturen. En biografi över Carl von Linné. Natur och Kultur. Stockholm, 2019.
4. Landell, N.E. Läkaren Linné. Medicinens dubbla nyckel. Carlsssons. Stockholm, 2004.
5. Uggla, A. Caroli Linnaei. Diaeta naturalis 1733. Linnés tankar om naturenligt levnadssätt. Almquist och Wicksells Boktryckeri AB. Uppsala, 1958.
6.  Drake af Hagelsrum, G. Linnés disputationer. Nässjö tryckeri. Nässjö, 1939.
7. Hjelt, O.E.A. Carl von Linnés betydelse som läkare och medicinsk författare. Almquist och Wicksell Boktryckeri AB. Uppsala, 1907.
8. Hjelt, O.E.A. Carl von Linné som läkare. Finska Litteratur-Sällskapets Tryckeri. Helsingfors, 1877.
9. Lindfors, A.O. Linnés Dietetik: Lachesis naturalis quoe tradit diaetam naturalem. Akademiska Boktryckeriet Edvard Berling. Uppsala, 1907.
10. Fredbärj, T. Linné som pediatriker. Föreningen Medicinhistoriska museets Vänner Årsskrift. 1955.
11. De Lacy, M.E.A. Linnean Thesis concerning Contagium vivum: The Exanthemata viva of John Nylander and its place in contemporary thought. Medical History 1995;39:159-85.
12. Wettrell, G. Carl Linnaeus – the young botanist, natural scientist and physician. Hektoen International Science, Winter 2024.
13. Wettrell, G. Carl von Linné som dietetiker och barnläkare. Läkartidningen 2025;122:822–824.