Cows in Gloucestershire were milked by men as well as by women; and men would sometimes milk cows with hands foul from dressing the heels of horses afflicted with what was called _grease_. With this _grease_ they infected the cows, and the pox which followed was pronounced by Jenner to have all the virtue against smallpox which the dairymaids claimed for cowpox. 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. REJECTION OF JENNER’S PRESCRIPTION.