Most of professional men are extremely reluctant in yielding assent to this statement. Some, indeed, reject it in the most unqualified terms. That Cowpox follows Cowpox appears certain, but that Cowpox should avert Smallpox, and not avert itself appears incredible. (P. 44.)
Here we see Pearson on the verge of discovery of the illusion, but with all his training and Yorkshire shrewdness he lost the scent, and allowed himself to be deceived; and not only deceived, but to become a prime mover in the deception of the world. Jenner felt the difficulty and replied—
Cheltenham, 27th September, 1798.
My dear Sir,—You may be assured that a person may be repeatedly affected, both locally and generally, by the Cowpox, two instances of which I have adduced, and have many more in my recollection; but, nevertheless, I have some reason to suspect that my discriminations have not been, till lately, sufficiently nice.... Certain it is, that the skin is always subject to the ulcerative effects of the virus; but whether the constitution can repeatedly feel the primary effects of it, I have experiments in view to determine. (P. 99.)
This passage is commended to those who hold with Mr. John Simon that Jenner delivered to the world “a Master-piece of Medical Induction,” the fruit of thirty years of incessant thought, watching and experiment. It is plain that in 1798 the very elements of the problem were by him undetermined, and the most obvious objections unforeseen and unconsidered.
Pearson’s strongest opposition was reserved for the asserted origin of Cowpox in Horsegrease. He said—
It has no better support than the coincidence in some instances of the two diseases in the same farm in which the same servants are employed among the Horses and Cows.
I have found that in many farms the Cowpox breaks out although no new-comer has been introduced to the herd; although the milkers do not come in contact with the Horses; although there are no greased Horses; and even although there are no Horses kept on the farm.
It appears that the Cowpox does not break out under the most favourable circumstances, if it be occasioned by the Grease. “I have had,” writes Sir Isaac Pennington, Cambridge, 14th September, 1798, “Dr. Jenner’s book some weeks, and the particulars stated in it are really astonishing. I have made inquiries upon the subject at Cottenham and Willingham, in which two parishes 3000 milch Cows are kept; also a great many Horses of the rough-legged cart kind (much liable to the scratches or grease) half the parishes being under the plough, and the men much employed in milking. But I cannot find that any pustulous eruptions on the teats of the Cows, or on the hands of the milkers, have ever been heard of.” (P. 82.)
In the opening of his Inquiry, Pearson was good enough to say of Jenner, “I would not pluck a sprig of laurel from the wreath that decorates his brow”; but, disputing the origin of genuine Cowpox in Horsegrease, he might have asked himself, what sprig of laurel he had left. That Cowpox originated in Horsegrease was not Jenner’s discovery. As Pearson ascertained in the London milk farms, “There was such a notion entertained in several parts of the country, whatever might be its foundation.” (P. 86.) But the definition of Horsegrease Cowpox as the form of Cowpox that justified the faith of the country-folk in the power of the disease to avert Smallpox, was Jenner’s solitary distinction—the principle and motive of his Inquiry, which, to prove fallacious, was to extinguish his title to regard. Cowpox apart from Horsegrease was clearly taught by Jenner to have no influence on the constitution, and to be attended with no erysipelas. “Let me call your attention,” he wrote to Pearson, 27th September, 1798, “to a similarity between the Smallpox and the Cowpox when inoculated. The symptoms of absorption first disturb the system, and, secondly, the system feels the consequences of the local sores. Exactly so with the Cowpox; and as the Cowpox inflammation is always of the erysipelatous kind, when it spreads over the skin to any great extent, it produces symptoms not unlike the confluent Smallpox.” (P. 100.)