[tok-sin-an-ti-tok-sin, -an-tee-, -an-ti-tok-sin, -an-tee-] 
| a mixture of toxin and antitoxin, formerly used to induce active immunity against certain diseases, esp. diphtheria. |
toxin-antitoxin n.
A mixture of a toxin and its antitoxin with a slight excess of toxin, formerly used as a vaccine.