With respect to the opinion adduced, that the source of the infection is a peculiar morbid matter arising in the Horse, although I have not been able to prove it from actual experiments conducted immediately under my own eye, yet the evidence I have adduced appears sufficient to establish it. (P. 43.)
Evidence adduced! Of evidence there was none. The farmers might be right in their opinion that Cowpox sprang from Horsegrease, but opinion was not evidence, nor even such assurance as this of Jenner’s—
I feel no room for hesitation respecting the common origin of the disease, being well convinced that it never appears among the Cows unless they have been milked by some who at the same time has the care of a Horse affected with diseased heels. (P. 44.)
But not even to this conviction did he adhere. “It was highly probable,” he thought, “that not only the heels of the Horse, but other parts of the body of that animal, are capable of generating the virus which produces the Cowpox”—
An extensive inflammation of the erysipelatous kind appeared without any apparent cause upon the upper part of the thigh of a sucking Colt, the property of Mr. Millet, a farmer at Rockhampton, the inflammation continued several weeks, and at length terminated in the formation of three or four small abscesses. The inflamed parts were fomented, and dressings were applied by some of the same persons who were employed in milking the Cows. The number of Cows milked was 24, and the whole of them had the Cowpox. The milkers, consisting of the farmer’s wife, a man and a maid-servant, were infected by the Cows. The man servant had previously gone through the Smallpox, and felt but little of the Cowpox. The servant maid had some years before been infected with the Cowpox; and she also felt it now in a slight degree. But the farmer’s wife, who had never gone through either Smallpox or Cowpox felt its effects very severely.
That the disease produced upon the Cows by the Colt, and from thence conveyed to those who milked them, was the True and not the Spurious Cowpox, there can be scarcely any room for suspicion; yet it would have been more completely satisfactory had the effects of variolous matter [Inoculation with Smallpox] been ascertained on the farmer’s wife; but there was a peculiarity in her situation which prevented my making the experiment. (P. 62.)
Spurious Cowpox! What was Spurious Cowpox? Here is Jenner’s answer—
Pustulous sores frequently appear spontaneously on the nipples of the Cows, and instances have occurred, though very rarely, of the hands of the servants employed in milking being affected with sores in consequence, and even of their feeling an indisposition from absorption. These pustules are of a much milder nature than those which arise from that contagion which constitutes the True Cowpox. They are always free from the bluish or livid tint so conspicuous in the pustules of that disease. No erysipelas attends them, nor do they show any phagedenic disposition, as in the other case, but quickly terminate in a scab without creating any apparent disorder in the Cow. This complaint appears at various seasons of the year, but most commonly in the spring, when the Cows are first taken from their winter food and fed with grass. It is very apt to appear also when they are suckling their young. But this disease is not to be considered as similar in any respect to that of which I am treating, as it is incapable of producing any specific effects upon the Human Constitution. However, it is of the greatest consequence to point it out here, lest the want of discrimination should occasion an idea of security from the infection of the Smallpox, which might prove delusive. (Pp. 7 and 8.)
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—