I really like this blog post reviewing the discovery of botulinum toxin by Rebecca Kreston: “The Bad Sausage & The Discovery of Botulism”.
Two years later, he published a second monograph chronicling the outcomes of 155 cases, speculating on the mechanism of what he would dub “the fat poison.” Kerner administered extracts of spoiled sausage mixed with honey to a menagerie of small captured animals – including flies, locusts, snails, birds, frogs, rabbits, and cats – finding identical presentations of “sausage poisoning” in fly and frog alike (2). He also made small incisions in the thighs of a rabbit and cat, daubing the exposed tissue with sausage extracts and found that the “fat poison” brought about a localized paralytic effect with complete recovery of the animals. Kerner also poisoned himself. Placing just a few scant drops of extract on his tongue, he noticed a “feeling of contraction and choking in the area of the larynx … some drops of the acid brought onto the tongue cause great drying out of the palate and the pharynx.”(2) The extract tasted sour, much like the spoiled sausages.
All of this unfolded in the 1820s.