Probably his most significant contribution was the development of a method of vaccination against anthrax. However, credit for creation of the anthrax vaccine went to Louis Pasteur, following Pasteur's celebrated demonstration with the vaccine on sheep at Pouilly-le-Fort in 1881. At Pouilly-le-Fort, Pasteur used a vaccine attenuated by potassium dichromate, employing a process similar to Toussaint's, who had published a means of attenuation by another antiseptic, carbolic acid. Pasteur never gave proper credit to Toussaint and his discovery. Pasteur's nephew, bacteriologist Adrien Loir (1862-1941) was aware of Toussaint's work with the vaccine, of which he documented in the 1938 treatise- A l'ombre de Pasteur (In the Shadow of Pasteur).
From 1881, Toussaint was in declining health, reportedly from a nerve-related disease. He died on 3 August 1890 at the age of 43.