Abstract
Antitoxoplasma globulin was labelled with fluorescein and was used to stain Toxoplasma gondii organisms in smears of peritoneal exudate. The evidence indicates that this staining was due to an antigen-antibody reaction at the cellular level. Methods are presented for handling the organisms so that they can be stained over a period of several months. Some general characteristics of the antigen system involved are described.