Observations on the surface coat of Blastocystis hominis.

The surface coat of Blastocystis hominis was studied in the electron microscope. In some cells the surface coat was seen in two layers; the external layer was more electron-dense and fragmented than the internal layer. It appears that the surface coat is being continuously formed by the parasite and shed in the environment. The fibrillar material of the surface coat attaches to the bacteria, in some cases, completely surrounding them, possibly causing cytoplasmic damage to the bacterial cell as indicated by loss of electron density.