Saturated Salt Flotation

Method

• A small amount of feces (a pea to grape size, about 1 gram) is mixed with about 10 ml of flotation medium and poured into a tube so that the liquid comes just over the top of the tube. The mixture is allowed to sit for about 15 min while the eggs float to the top and the rest of the fecal matter sinks to the bottom. A cover slip can be placed on the top of the tube before the incubation period starts or can be applied at the end. The cover slip is then transferred to a microscope slide.
• Commercial devices have a sieve incorporated into the tube to keep large particles from floating up and sticking to the coverslip. See image below of some commonly available commercial fecal devices.



USES: This method will recover most nematode eggs and protozoan cysts, however many trematode and cestode eggs, as well as Giardia cysts will not be recovered.

 

Specific Gravity of Some Helminth Eggs as Determined Using Sucrose Density Gradient Centrifugation*

Species	Mean Specific Gravity	Range
Ancylostoma caninum	1.0559	1.0549 - 1.0573
Toxocara canis	1.0900	1.0791 - 1.0910
Toxocara cati	1.1005	1.1004 - 1.1006
Taenia sp.	1.2251	1.2244 - 1.2257
Physaloptera sp.	1.2376	1.2372 - 1.2380
ZnSO4 Solution	1.18
Saturated salt or sugar	1.20

*from David and Lindquist, 1982. J. Parasitology 68:916-919.