Nothing could be more explicit. COWPOX was of two kinds--True and Spurious. The Spurious consisted of pustular sores which appeared spontaneously on the nipples of Cows, and was of no avail against Smallpox: the True Cowpox, on the other hand, was not a disease of the Cow, but of the Horse transmitted to the Cow. It is of prime importance to bear this distinction in mind; for if it is not borne in mind, much that remains to be told must appear confused or unintelligible. As we have seen, it was the belief of the dairymaids that if they caught Cowpox they would never afterwards catch Smallpox. Medical men in practice in Gloucestershire ridiculed the dairymaids’ belief. They said-- “We know that such is the dairymaids’ faith, but it is mistaken; for we know dairymaids who have had Cowpox and afterwards had Smallpox in spite of their Cowpox.” At this point Jenner intervened, saying-- “Let us distinguish. Eruptions contracted in milking are indiscriminately described as Cowpox by dairy-folk; but there is an eruption attended with erysipelas and fever which has all the virtue they claim for it. This variety of eruption does not originate on the Cow, but is communicated to the Cow from the Horse. Thus the dairymaids are right and they are wrong. They are right when the pox they catch is derived from the Horse through the Cow: they are wrong when the pox they catch originates on the Cow without the Horse. In short Cowpox proper is of no avail against Smallpox. It is Horsegrease Cowpox that is of sovereign and infallible virtue. Any maid who receives HORSEGREASE COWPOX into her veins is, as she believes, for ever after secure from the infection of Smallpox.” Let us therefore bear in mind that Jenner’s prescription was not Cowpox but HORSEGREASE COWPOX. It is a point to be insisted upon; for, as we shall see, it was lost from sight, and kept out of sight, to the utter confusion of the question. * * * * * We now come to Jenner’s Cases of Horsegrease--for not only were farm-folk reputed secure from Smallpox by reason of Cowpox, but farriers likewise in consequence of infection with Horsegrease. XIII.--THOMAS PEARCE, son of a Farrier. In consequence of dressing Horses with sore heels at his father’s when a lad, had sores on his fingers which suppurated, and occasioned pretty severe indisposition. Six years afterwards, Jenner inoculated him repeatedly with Smallpox, but only produced slight inflammation, and exposed him to the contagion of Smallpox without effect. On this Case Jenner observed-- It is a remarkable fact, and well-known to many, that we are frequently foiled in our endeavours to communicate Smallpox by inoculation to blacksmiths, who in the country are farriers. They often, as in the above instance, either resist the contagion entirely, or have the disease anomalously. Shall we not be able now to account for this on a rational principle? XIV.--JAMES COLE, Farmer.