The Biology of the Goat Laboratory

How to do your own fecal exams

Making a Flotation Solution

We take advantage of specific gravity in order to view the eggs of parasites. Specific gravity is defined as the density of one fluid compared to water so it is sometimes called relative density. Pure water has been assigned a specific gravity of 1.0. We compare the density of all other solutions to water. Anything with a density of less than 1.0 will float in water and anything with a density of greater than 1.0 will sink in water.

Specific Gravity Parasite eggs have a specific gravity of about 1.1 to 1.2. If you put eggs in water they will sink. In order to make the eggs float we need a solution that has a specific gravity that is higher than 1.2. Fecal debris has a specific gravity of 1.3 or higher. If the flotation medium has too high a specific gravity then the debris will float along with the eggs which will make the eggs hard to see and the high concentration will distort the eggs.

We make a dense solution by dissolving sugars or salts in water. If compounds that are denser than water are dissolved in water the specific gravity increases. In laboratories a commercial solution of sodium nitrate is used which has a specific gravity of about 1.25, making it ideal for floating parasite eggs. Sugar can be used but it is sticky and it is hard to get the specific gravity above 1.2 therefore larger eggs will not float. Regular table salt is the least desirable because it corrodes equipment and forms crystals which distorts the eggs. In addition, the specific gravity of table salt can never go above 1.2 so larger eggs will not float.

Epsom salt There is one very common salt, called magnesium sulfate, which is found in most homes and is inexpensive to buy. Commonly called Epsom Salt, magnesium sulfate works very well for a flotation solution since it has a specific gravity of 1.296.

To make a solution, start with a clean, glass quart jar and fill it about half-full of warm water. Begin adding epsom salt, about a quarter cup at a time, stirring until each addition is completely dissolved. Keep doing this until the salt no longer dissolves and there is a few crystals at the bottom. Your quart jar will be almost full by then. Let the jar sit overnight and you will notice that most of the crystals will have dissolved. You may see a few crystals at the bottom that have not dissolved which means that you have a saturated solution. Keep the solution well-sealed and it will last for months.

Next Prepare your sample.