Scientists recently discovered how to examine specimens collected by Charles Darwin without opening the jars they’re stored in. They used lasers to analyze the preservation liquids within these jars. This method enables safer study of delicate collections that have remained untouched for almost two centuries.
Darwin’s journey on the HMS Beagle from 1831 to 1836 was pivotal in forming the theory of evolution. During this trip, he collected various animals, now preserved at the Natural History Museum in London, including mammals, reptiles, and jellyfish.
In the past, figuring out what chemicals preserved these specimens often required opening the jars, risking damage or contamination. Thankfully, a new technique called Spatially Offset Raman Spectroscopy (SORS) provides a solution. This portable method allows researchers to measure the light scattered by a laser to reveal the chemical makeup of the liquids inside the jars.
Traditional Raman spectroscopy struggles with sealed jars since the glass can distort readings. SORS solves this by taking multiple readings from different angles, allowing scientists to separate the glass interference from the deeper signals.
This technology, initially developed for airport security scanners, has been adapted for museum use. Researchers examined 46 specimens collected during Darwin’s Galápagos expedition and those brought in by other early naturalists. They found that the preservation methods differed significantly depending on the species and the time period. For example, mammals and reptiles were often preserved in formalin and then stored in ethanol, while invertebrates were preserved in a variety of solutions, including formaldehyde or mixtures with glycerol.
Interestingly, historical preservation practices weren’t uniform. Recipes varied widely, ranging from alcohol solutions to those containing formaldehyde or even picric acid.
Thanks to SORS, researchers identified preservation fluids in about 78.5% of the samples, with some uncertainty in another 15%. They also distinguished between types of glass and plastic used in containers, offering insights into historical storage practices.
Dr. Sara Mosca from the Central Laser Facility highlighted the importance of this method: “Understanding what preservation fluid is in each jar meant opening them, which risks evaporation and contamination.”
With museums housing over 100 million biological specimens in liquid, knowing the exact chemical composition of preservation fluids becomes crucial for maintaining them. Non-invasive tools like SORS could help museums monitor collection conditions without risking damage to historically sealed containers. This advances our ability to preserve invaluable scientific heritage for future studies.
For more on this innovative technique, check out the study published in ACS Omega.
