HORSEGREASE COWPOX.
According to Jenner, then, the dairymaids were right, and they were wrong. They were right when the pox they caught was derived from the horse through the cow; they were wrong when the pox they caught originated on the cow without the horse. He thus discriminated a double pox—cowpox of no efficacy against smallpox, and horsegrease cowpox of sure efficacy.
Further, in this connection, it is to be observed, that farriers believed that when they got poisoned in handling horses with greasy heels, they too, like the dairymaids, were safe from smallpox.
It is not therefore for cowpox, but for horsegrease cowpox that Jenner is answerable. In cowpox he had not, and could have no faith.
In 1798 Jenner published his famous Inquiry, a treatise much more spoken of than read, wherein he distinctly set forth the origin of his chosen prophylactic. It was not, I repeat, cowpox: it was horsegrease cowpox. He carefully discriminated it from spontaneous cowpox, which, he said, had no protective virtue, being attended with no inflammation and erysipelas, the essential sequences of inoculation with effective virus.