Henrik Gahn tries to awaken Linnaeus’s memory of him with a long introduction, saying that he left Sweden a year ago and that an unfortunate shipwreck and the late autumn led him to overwinter in Göttingen.
In Hamburg he got to know Hermann Samuel Reimarus, who had refuted the Viennese Heinrich Johann Nepomuk von Crantz’s stupid botanical writings, and also Joachim Friedrich Bolten, who had written to Linnaeus concerning a new zoophyton, which was certainly nothing other than a variety of Vorticella ovifera in George Edwards, A natural history of uncommon birds and which Gahn had seen later when visiting Joseph Banks, all with elongated capitula and caught in the South Seas. In both Lübeck and Hamburg Gahn had seen specimens of Oculus mundi, and had also conducted experiments, finding that they were nothing but porous stone that absorbed air and then released air bubbles and at the same time became transparent. In Göttingen, Gahn attempted to improve himself through the German medical literature, the best opportunity being through the magnificent library that Otto von Münchhausen had founded. Botany had improved considerably since Andreas Murraytook over and Murray worked like a slave to get his little garden in order. He already had a considerable collection of plants. Otherwise, Gahn found the Germans exactly as Linnaeus had described them: One cannot look for inventions or ingenium among them but they are extraordinarily industrious and know how to improve upon the discoveries of others with great diligence. When Gahn left Göttingen he first visited the mines in Hartz, where he found a climate similar to that in Sweden and with Swedish plants, and then he arrived in Pyrmont. All the experiments that the Germans had conducted with Pyrmont water were false and had also led to practical medical errors. Gahn found that the iron contained in the water was not dissolved by any acid or alkali but by the so-called Aër fixus Halesii [carbonic acid ]. This fluidum, that is incorrectly called air, is fully capable of dissolving iron, and Gahn believes that it forms all mineral waters. A pharmacist in London had recently performed the same experiment. When the very least warmth is applied the air is released and at the same time the iron sediments to the bottom. Consequently, when Pyrmont water is retailed it seldom has any particular content of iron and has almost the opposite effect than at the spring itself since the Sal amarum has a laxative effect but no longer gives strength when the iron has disappeared. Close to the spring is the so-called sulphur valve containing a poisonous air similar to that in Grotta del Cani in Italy. After a few deductive experiments, Gahn found that it was incorrect to believe that it was evaporated sulphur but was nothing more that this Aër fixus, which is an unsuitable fluidum for animals to respire. The warmth from the air separates it from the actual spring water when it leaves the ground and, thus, if one leans over the spring one will be killed in the same way as in the sulphur valve. Iron filings placed in the water do not leave the slightest trace of iron, but when this mixture was placed overnight in the sulphur valve it received a complete taste of mineral water and was coloured by A[cidum] Gallarum. Gahn believes that this Aër fixus, together with a bag containing bog iron, explains the manufacture of Pyrmont water, and does not originate from a neighbouring mountain where the Germans have suspected iron but have found nothing but sandstone. Gahn also visited the famous economist Otto von Münchhausen, who lived not far from Pyrmont. Being a disciple of Linnaeus, Gahn was fairly well received. Gahn had never seen such a large collection of trees and saw from the fields that he was as good in economy as he was as a writer. In Holland, Gahn met Johannes Burman, Nicolaas Laurens Burman and Adriaan van Royen and David van Royen. Their gardens were now not what they were; both George Clifford’s garden [Hartecamp] and Herman Boerhaave’s garden had been sold and dispersed, and the best is perhaps the one Herman Martin Wilhelm Schwenck had in The Hague. Wouter van Doeveren was occupied with writing a description of Petrificates that he had found near Gröningen and promised to send Linnaeus the book when ready. However, Gahn was unable to visit the celebrated Hieronymus David Gaub; he had recently introduced a new medicine called Lopezii, which is excellent against all diarrhoeas caused by weakness of the fibres, in the colloquial also called Phthisicorum. This medicine is still so scarce that it is not sold in the pharmacies but nonetheless Gahn was able to acquire a small bit that will be sent to Linnaeus at the first opportunity. The root is taken from the island Malacca to Batavia but some believe it to come first to Goa, but there the plant is completely unknown. It tastes almost of nothing, but a half drachma every 3 or 4 hours almost always cures the worst diarrhoea by the second day. This has been described in a book published by Gaub, Adversariorum varii argumenti.
Gahn also tells Linnaeus about another medicine with almost the same effect that John Pringle in London had introduced, called Colombo after Ceylon’s capital, from where it is fetched. It is also a root of an unknown plant. As soon as Gahn finds out more, he will inform Linnaeus, but knows that it is fairly specific in treating diarrhoeas in children, but also effective in after dysenteries. Pringle had himself told Gahn that he had found the best effect of it also in nausea and other conditions. The dose is one-half drachma, like the former, two or three times a day.
When in The Hague, Gahn heard from a Pieter Bosch{bioBoschP} that no medicine was better for treating the Dutch women’s diseases. Gahn apologises to Linnaeus for having written so much about this. Gahn had heard that Linnaeus was preparing a new edition of Materia Medica and thought that these two roots would find space therein. Postage is so impossibly expensive in England that Gahn thought he would have to find a vessel bound for Stockholm to take the roots, after which Gahn’s brother [Johan Gottlieb Gahn] would take them to Uppsala.
Gahn had arrived in London about one month previously, just in time to see numerous collections and discoveries made by Daniel Solander and Joseph Banks. Gahn is convinced that they have, or will, give Linnaeus everything, so Gahn need not describe anything. They were planning a new journey, to be started in March. Gahn had hoped to be able to join the expedition as Solander had half promised him. So now Gahn plans to improve his medical knowledge by visiting the numerous large hospitals, either in London or in Edinburgh. During the winter Gahn had written to Jonas Sidrén, but did not know if the letter had arrived. Gahn asks Linnaeus when the Medical Faculty [at the University of Uppsala] will have its next promotion. Gahn hopes that he will not be forgotten in that context and that his rapid departure would not be a disadvantage.
In closing, Gahn recalls the happy days he had at Hammarby and sends his greetings to Linnaeus’s family, his wife [Sara Elisabet Linnaea], the young daughters [Sara Christina Linnaea, Sophia Linnaea] and the young professor [Carl Linnaeus the Younger] .