The amount of anti-toxoplasma antibodies in a specified sample of serum (the clear liquid that separates from blood after it has clotted completely, i.e. blood plasma from which fibrinogen has been removed) expressed as the last dilution of serum at which a positive result could be obtained. An anti-toxoplasma antibody is an immunoglobulin molecule possessing a specific amino acid sequence that binds to a specific antigen found on or in the parasite toxoplasma, a genus of sporozoa the only species of which is Toxoplasma gondii that are intracellular parasites of many organs and tissues of birds and mammals, including humans. A parasite is an organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host and possibly causing damage to that host. An antigen is a substance introduced into an organism which initiates an immune response, including the production of the very antibodies which bind to it in an effort to destroy it.