Unlocking Darwin's Secrets: Lasers Reveal Contents of 200-Year-Old Specimen Jars

For 200 years, preserved specimen jars from Charles Darwin's Galapagos voyage have remained unopened in London's Natural History Museum (NHM) archives. Scientists have now used lasers to examine their contents without opening them.

The Challenge of Unknown Preservation

Understanding the preservation fluids within these specimens is critical for their care and future research.

Historically, opening the jars risked evaporation, contamination, and environmental damage to the specimens.

Various fluids, including alcohols (ethanol, methanol) and formaldehyde, have been used in preservation, leading to diverse and often unknown chemical compositions within collections. Identifying these fluids is essential for proper conservation.

Non-Invasive Analysis: Spatially Offset Raman Spectroscopy (SORS)

A team of scientists, including NHM research technician Wren Montgomery and physicist Sara Mosca, utilized spatially offset Raman spectroscopy (SORS) to analyze the jars. Traditional Raman spectroscopy was unsuitable, as its signal is dominated by the container's surface.

SORS overcomes this by taking multiple laser measurements at different offsets, allowing for the chemical signatures of both the surface and subsurface to be revealed.

This innovative approach provided a safe and effective way to probe the hidden contents of the historic jars.

Unveiling Darwin's Secrets

Applying SORS to Darwin's collection enabled researchers to accurately identify the preservation fluids in nearly 80 percent of the jars. An additional 15 percent were partially identified, with only 6.5 percent remaining unidentifiable.

The study found that mammals and reptiles were typically 'fixed' with formalin and then suspended in ethanol. Invertebrates, such as jellyfish and shrimp, were stored in formaldehyde or buffered formaldehyde, sometimes with added glycerol or phenoxetol to enhance tissue integrity.

A Global Solution for Museum Collections

This technique has significant implications beyond Darwin's collection. Museums worldwide house over 100 million fluid-preserved specimens that are often too fragile to open.

SORS provides a method to monitor and care for these invaluable specimens without compromising their integrity.

The groundbreaking research was published in ACS Omega, offering a new standard for the preservation of historical scientific collections.