Wet Specimen Preservation



A Brief History of Wet Specimen Preservation:

  • Wet specimens were first introduced as a preservation method for small animals such as fish, turtles, and rodents in the 16th Century by the well-known Amsterdam Anatomist Frederik Ruysch. Ruysch began testing preservative fluid techniques shortly after realizing that human cadavers were not only expensive study tools and difficult to source, but they did not stand the test of time in the summer months. Without proper preservation, specimens would quickly decompose unless in the cold conditions of a harsh winter.

  • Before modern preservatives were accessible, specimens were often stored in Brandy, Rum, or other spirits. Ruysch established a formula called “Liquor Balsamicum” although the details of this solution were not disclosed until 2006.

  • With well-sealed lids not readily accessible, these specimens were sealed with pig fat or skin, which was then burnt and stretched over a container to prevent leaks and reduce air exposure. This allowed fellow scholars and students to further the practice of studying organisms both big and small.

  • Early wet preservation included spices such as clove, cinnamon, cassia, or cardamom. These spices were used to help with the smell of the decay, as well as an antimicrobial agent to slow down the decomposition process.

  • It wasn’t until the 19th century that formaldehyde was introduced, with Ethyl and Rubbing Alcohol being later included in the making of wet specimens.

What makes wet specimens different
than other preservation methods?

  • While there are many preservation methods, such as taxidermy, skeletonization, and mummification, wet specimens are distinct because they preserve an organism in its entirety. Wet specimens keep a complete, lifelike, and detailed specimen, keeping soft tissues and inner organs preserved for years to come.

What you’ll need to make a wet specimen:

-10% buffered formaldehyde (formalin) Ethyl can be used instead, but preserves by dehydrating rather than stiffening

- Glass container with an airtight, chemical-resistant seal

- 70% isopropyl alcohol

- 18-26 Gauge Hypodermic needles

- Heavy-duty nitrile gloves

- Chemical splash goggles

- Respirator with organic vapor cartridges to protect against chemical fumes

- A large, well-ventilated space to work on your wet specimen

- Fluid absorbent pads to catch any spilt chemicals

- Wire (optional, but helpful when posing specimens in the fixation process)

- Scalpel

 

HEALTH DISCLAIMERS:

  • Improper handling of formaldehyde can cause cancer and birth defects.
  • DO NOT WORK WITH FORMALDEHYDE-RELATED PROJECTS IF YOU ARE PREGNANT OR TRYING TO BECOME PREGNANT.
  • OSHA Guidelines state that it is safe to have up to 15 minutes of unprotected exposure to formaldehyde per day. It is recommended to stay cautious and ALWAYS wear a mask when handling formaldehyde.
  • NEVER work with formalin around children or animals.
  • DO NOT attempt to hold your specimen while injecting. You run the risk of stabbing or injecting yourself.

HOW TO MAKE A WET SPECIMEN:

STEP ONE: Clean and Prep
  • Gently wash your specimen with water to remove any dirt, debris, or other surface imperfections. Make sure your specimen is thawed before this step if it was previously frozen.
STEP TWO: Injection
  • This step is crucial to prevent rot and decomposition. Inject your specimen with formalin or high proof ethanol using an 18-26 gauge needle into the limbs, brain, nose, eyes, ears, and mouth, until slightly plump. Be careful not to over-inject! When preserving a larger specimen such as a fetal cow, pig, etc., it is recommended to inject in approximately 1” increments to ensure proper preservation of larger organs and tissues. For example, an average mouse will take about 5-7cc of fluid. An average adult rat will take about 30cc of fluid.
STEP THREE: Soaking your specimen
  • Submerge your injected specimen in formalin and let it soak. It is recommended to let your specimen soak for 1-2 weeks for smaller animals and up to 5-6 weeks for larger animals.
  • This will help formalin seep into the specimen through the skin and previous injection sites using the fluid exchange process. Lightly shake your specimen in its jar every 3-5 days to encourage any small air bubbles or preexisting fluids to make their way out of the specimen.
STEP FOUR: Rinse
  • Remove your specimen from the formalin and soak it in distilled water for 24-48 hours to remove any excess chemicals.
STEP FIVE: Final Preservation
  • Rinse off your specimen once more and place it in its final display jar. Then fill your jar with 70% Isopropyl Alcohol for long-term storage.

WET SPECIMEN CARE

  • Always store your specimens away from sources of heat. Including fire, open flames, direct sunlight, radiators, etc. Alcohol and formalin are highly flammable, so don’t store them near a stove or fireplace, don’t smoke around them, etc. Use common sense to decide where in your home your specimens will be safest.
  • Sunlight will degrade the specimens.
  • Store away from pets and children.
  • Never EVER eat, drink, or allow anyone else (human or animal) to eat or drink any part of your specimen, including any of the liquid solutions. If your jar breaks, use gloves to carefully pick up the large glass pieces and specimen, and dispose of broken glass immediately. Absorb any liquid with cat litter or sawdust (along with sweeping up any leftover glass) and dispose of it.

WET SPECIMEN FAQ'S

Can I use plastic containers?

Plastic is NEVER recommended. Formalin is a professional-grade incredibly toxic chemical that can easily eat through materials other than glass. If you are insistent on using plastic, it is important that you test a small amount of formalin before storing your specimen long term in a plastic container, as formalin breaking down the plastic can cause it to melt or leak.

Can I put my specimen directly into Isopropyl Alcohol instead of using formalin?

No. Using only Isopropyl Alcohol will cause your specimen to deteriorate or rot from the inside out. Once your specimen starts to decay, there is no way to reverse any damage done to the specimen. Fixing a specimen with formalin is a must to guarantee the success of a long lasting wet specimen.

What if my wet specimen floats?

A specimen floating means one of two things. It is either preserved incorrectly and beginning to decay, or air has been trapped somewhere in the specimen, causing it to stay afloat. Use a scalpel to make a small incision in your specimen, then shake and let it sit for 24-48 hours. If it starts to sink, you’ll know you’ve gotten rid of any potential air pockets. If it continues to float after repeated attempts to redeposit formalin, it is recommended to dispose of your specimen, as it is more than likely decayed tissue that will break down your specimen over time.

Can Formalin be reused?

While the short answer is yes, studies show that it is only recommended to be reused up to three times. Recycled formalin is contaminated after its first use, making active ingredients diluted until it is no longer effective. Recycled formalin should ONLY be used for soaking your specimen. When injecting, it is important to use fresh formalin to avoid clogging of the syringe and guarantee the best preservation possible for your specimen. Properly dispose of your formalin when it becomes murky or turns to a muddy brown color.

How do I dispose of Formalin?

Spilled or used formaldehyde is hazardous waste and must be handled as a solid waste under RCRA. Find a hazardous waste treatment facility in your area and reach out for proper protocols when you have a jar or two full of formalin that needs to be disposed of. There may be a fee associated with this disposal. Pay the fee. NEVER dump formalin or anything containing formaldehyde into the trash, ground, sewer, sink, shower, toilet, or other water sources. Formalin will get back into our water stream and can prove fatal to humans and animals if you do not act responsibly. You may also be able to contact a local funeral home and pay a small fee for them to dispose of the formalin for you.

How do I know which size needle to use when injecting?

Most specimens take an 18-26 gauge needle. There can be some variation in the size of the needle as larger specimens do best with an 18 gauge needle, and smaller specimens do best with a 26 gauge needle.

Where can I purchase wet specimen materials?

Formalin, heavy-duty nitrile gloves, gauged hypodermic needles, chemical splash safety goggles, isopropyl alcohol, reusable respirators, and 3M 6005 respirator cartridges are all available on Amazon! There are also many laboratory and scientific companies worldwide that can ship these same products to you!

Can I use any kind of respirator?

No. Respirators and corresponding filters are made differently depending on their purpose. Proper protective wear is essential. For Formalin or formaldehyde-specific projects, you will need a reusable respirator and specialized cartridges. The recommended cartridges to use are a 3M Formaldehyde Cartridge 6005 or 6075, or a Moldex Formaldehyde Cartridge. N95 masks do not protect you from exposure to harsh chemicals.

Can you preserve an already rotting specimen?

While most would assume roadkill or other found specimens are good to use, formalin cannot reverse decay. If your specimen is bloated, has a smell, discoloration, or slippage of hair, it will not stay preserved. Instead, it will continue to decay until it disintegrates.

How do you dispose of used needles and scalpels?

Needles must never be placed in household trash or recycling bins. Never attempt to bend, recap, break, or clip the needle off a syringe after it has been used, as it significantly increases your risk of accidental sticks. Always look up guidelines specific to your community, as regulations surrounding biohazard disposal can vary by jurisdiction. You can find specific disposal locations in your immediate area by using the Safe Needle Disposal search tool, which allows you to look up drop boxes and mail-back programs by zip code. It is recommended to dispose of sharps in an FDA-cleared sharps container. If one is unavailable, use an opaque, heavy-duty, puncture-proof plastic container with a screw-on lid (e.g., an empty liquid laundry detergent or bleach bottle).

Click here to read about safe needle disposal in your area.