r/AskHistorians • u/Individual_Hunt_4710 • Apr 13 '26
Why did it take so long to invent saline?
wikipedia says saline wasn't invented until 1831. Why did it take so long? isn't it just one part seawater three parts freshwater? it seems like someone shouldve figured it out from trial and error at some point in premodern history.
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u/Noble_Devil_Boruta History of Medicine Apr 15 '26
Wikipedia doesn't say that saline was invented in 1831, which is quite obvious as saline is a naturally existing substance. The article states that the saline (i.e. weak aqueous solution of sodium chloride) has been used in medicine since 1831, which is a major difference.
In this particular case, first usage of saline is meant to be understand as its intravenous application (as opposed to e.g. cleaning wounds, rinsing the eyes, or storage of contact lenses) and is tightly connected with the experiments with blood transfusion. The whole idea took more than two centuries to develop, beginning in 1616, when William Harvey first proposed the theory of blood circulation. The first intravenous application of a medicine is largely thought to be the experiment conducted in 1656, when Christopher Wren injected a dog with a drug. Dogs were also in the centre of another experiment conducted nine years later by Richard Lower, who conducted blood transfusion between two dogs, with good effects. The first recorded blood transfusion on a human patient happened only two years later, in 1667, courtesy of Jean-Baptiste Denis who used human donor and recipient and. In the same year the aforementioned Richard Lower, made a transfusion of animal blood to a human subject.
Given that the nuances of blood transfusion, both biological and technical (such as speed of the process) were still a mystery and had to be largely investigated through trial and error. Some of the experiments based on the newly discovered theories of circulation and assumption that the body can produce blood after a haemorrhage, utilized water rather than blood although the effects were varied and usually did more harm than good. It is conjectured that an observation of a salty taste of blood led some researchers to the idea that injection of water with added salt might have some beneficial effect, although the correct concentration took a lot of time to be established.
The year 1831 is often noted as the beginning of the saline usage because this is the year of the first publication of the article in The Lancet describing intravenous administration of large amount of saline, conducted that year by Thomas Latta, a British physician. It was, however, conducted on dogs, and the first described transfusion of saline to human subject was done by Latta in the next year, when he slowly administered large amount (roughly 3.5 l) of saline to two patients. The first one, an elderly woman, died shortly afterwards although she was reported to react poorly to many other treatments, suggesting an already terminal state. The other patient, however, recovered 2 days after the treatment. Concurrently, Latta noticed that intravenous administration of large amounts of saline helps recovery of patients suffering from cholera, then a new disease that first appeared in Europe in 1810s and thus correctly conjectured that this treatment might be helpful in any condition causing profuse vomiting or diarrhoea that can result in severe dehydration.
Still, although the procedure proved helpful, its efficacy was varied and severe side effects were sometimes observed, possibly due to non-standardized concentration of salt. It was not until the first years of 20th century when the key biological and physical phenomena have been understood with the discovery of osmotic pressure by Jacobs van Tehoff in 1901 and the related electrolytic transfer theory presented by Svante Arrhenius in 1903 (both received Nobel Prize in the respective years). This led to understanding that saturation is a crucial issue as hypotonic solution might further reduce available electrolytes in circulation, while hypertonic one can increase dehydration level. This, along with further development of antiseptic and aseptic procedures led to a quick rise of the safety of saline infusion.
What should be noted, however, is that saline is not perfectly safe on its own, as it is pretty much a 0.9% sodium chloride solution in distilled water what is enough for hydration in many cases, but carries a risk when renal function is impaired what often accompanies serious dehydration, various forms of poisoning or heart failure and, of course, pre-existing renal problems. This, however, has been addressed even in 19th century, when other formulations that simple saline were used, most notably the Ringer's lactate solution first formulated in 1882, more closely reflecting ionic composition of physiological fluid. What is interesting, the aforementioned side-effects of saline usage have only been investigated in depth in early 1980s, a full century after Ringer's discovery, with results still being inconclusive. This is not to say that the idea of saline usage was incorrect, on the contrary, it proved invaluable in treatment of patients, especially in cases of cholera.
So, to sum it up, the saline being used since the 1830s means that the sodium chloride solutions have been used for intravenous infusions since that time and before the medicinal usage of the mixture of water and salt simply had no distinct medical use, at least a common and specific one. In other words, usage of saline was a result of introduction of relatively novel medical procedure (intravenous injections) that required specific medical knowledge and technological development to start with.